It is not often that we confront the possibility that we are on the cusp of a completely new era, a fundamental reshaping of the international order.

But that is where the world stood in July 2018 as President Trump prepared to attend the NATO summit in Brussels. We may still be standing there today.

Hyperbole? It is tempting to dismiss such warnings as the ravings of those afflicted with Trump Derangement Syndrome, the condition allegedly caused by the belief that Trump is a uniquely damaging figure in American, and possibly world, history. And there is a tendency deeply embedded in human nature to disbelieve that things that seem impossible, that shake the foundations of the world we know, can actually occur.

But there is no point deluding ourselves. President Trump aspires to pull the United States out of NATO. He has actively contemplated such a step, speaking about it openly on numerous occasions. Many of his aides, deeply grounded in the traditional principles of U.S. foreign policy, which place high value on the Western alliance, fear he could act on it. And Russian President Vladimir Putin, NATO’s greatest foe, is licking his chops, wondering what more he can do to make his impossible dream a reality.

What the United States Gets From NATO

The founders of the North Atlantic alliance, and those who sustained it for seven decades, would be baffled by this turn of events.

From the signing of the North Atlantic Treaty in 1949, presidents from Harry Truman to Ronald Reagan to Barack Obama held forth about the essential nature of an alliance that served, during the Cold War, as a means of collective defense against Soviet aggression. The strategy, in Truman’s words, was that “If we make it sufficiently clear, in advance, that any armed attack affecting our national security would be met with overwhelming force, the armed attack might never occur.”

Since the breakup of the Soviet Union, NATO has also served as the mechanism for collective action to advance Western interests during conflicts in places as diverse as the Balkans, Afghanistan, and Libya. No less important, NATO has fostered the security component, supplemented in time by the political and economic achievements of the European Union, of a more integrated, less conflict-prone Europe. The success of NATO is inseparable from the advance of democratic values in Europe and globally, and the prosperity that has benefitted Europeans and Americans, for many decades.

Among NATO’s more recent achievements are its successful expansion to include former Warsaw Pact states of Central and Eastern Europe as well as the Baltic states freed from Soviet domination, the forging of partnerships with dozens of nonmember states across Eurasia and the Mediterranean, and, perhaps most fundamentally, the establishment across its now 29 members of a deeply held commitment to its sanctity of purpose.

American officials tend to play down the notion, but one can scarcely dispute that NATO is a U.S.-dominated construct. While unanimity within the alliance is required for major decisions, the United States has maintained a preeminence in alliance policies, as other members, even if at times fitfully, sublimated their national policies to American views. Tens of thousands of U.S. forces at bases across Europe have facilitated the projection of American power on the other side of the world in ways that would be unimaginable otherwise.

Yet NATO has come to America’s defense as well. In the only example of NATO’s invocation of its Article 5 provision—which holds that an attack on one nation be deemed as an attack on all—NATO nations rallied after the September 11 terrorist attacks and sent soldiers to fight alongside American troops in Afghanistan. More than 1,000 of them have paid with their lives.

Like any alliance, though, it has had its share of internal conflicts, even contradictions. Some NATO members have resented the dominant U.S. role, or pursued different approaches toward their own relations with the Soviet Union, and later the Russian Federation. American complaints about NATO members not meeting their defense spending targets are not new. In addition, some NATO members, notably Hungary and Turkey, and arguably Poland as well, have, in recent years, weakened their democratic institutions to a significant degree, injecting new tensions.

But despite all of its ups and downs through the decades, no serious analyst could call into question the alliance’s fundamental successes, nor the degree to which it has dramatically advanced U.S. interests. It is such an entrenched part of a consensus American national security outlook and, indeed, of the international structures we have come to rely upon, that the very notion of the United States withdrawing from the alliance has been utterly unthinkable.

Until Trump.

The Anti-NATO President

By his own account, Trump does not see, understand, or value any of the benefits of the NATO alliance, which throughout his presidential campaign he called “obsolete.” He has made this clear on many occasions; frankly, he does not appear to believe in any alliances whatsoever. Alliances, in his view, are for suckers. They require the United States to subordinate its own interests and, in doing so, allow other nations to take advantage of us. In the case of NATO, he has focused particularly on the false notion that other members are obligated to pay the United States for the protection it provides them, and are delinquent for not doing so. This theme comes back again and again, such as when Trump declared at a campaign rally in West Virginia last August, “Our allies treat us worse than our enemies.”

The Trump go-it-alone approach (one can hardly call it a strategy) is most prominent in his attitude toward international trade. He withdrew from the Trans-Pacific Partnership, has threatened to do the same with NAFTA and the WTO, and has escalated innumerable tariff battles with trading partners across the world. So convinced is he of the nefarious designs of all who do business with the United States, and of the effectiveness of his own high-pressure negotiation tactics, that, at odds with all of his predecessors, he has embraced trade wars as a favored tactic and declared them “good and easy to win.”

In a startling essay published in The Wall Street Journal in the spring of 2017, then-National Security Adviser H.R. McMaster and then-White House Chief Economic Adviser Gary Cohn attempted the impossible by trying to impute some strategic logic into Trump’s childish impulse to hoard all his toys. Entitled “America First Doesn’t Mean America Alone,” the piece was an incoherent mess, and it is difficult to believe that either author—both confirmed internationalists—truly subscribed to their own thesis.

The argument put forth by McMaster and Cohn began with the proposition that all nations act in their own interests. But that rather standard realist perspective soon gave way to an open disdain for international partnerships. The Trump Administration, McMaster and Cohn wrote, welcomes a world of dog-eat-dog competition, in which every nation competes with every other, all the time, in every sphere. Trump, his advisers claimed, understands that “The world is not a ‘global community’ but an arena where nations, nongovernmental actors and businesses engage and compete for advantage. . . . Rather than deny this elemental nature of international affairs, we embrace it.” The quaint notion of making compromises with allies to advance common interests or, heaven forbid, common values, was treated as so much naïve gibberish.

The implications of this worldview, for the most central alliance in U.S. foreign policy, were ominous and unmistakable. Why, the authors strongly imply, should the United States place limits on its own freedom of action and take on obligations to expend blood and treasure to protect other nations, when its international philosophy is governed by zero-sum logic?

Nothing, however, more directly challenges that way of thinking than NATO’s Article 5 obligation for collective defense.

McMaster and Cohn’s article was essentially trying to explain why Trump, attending his first NATO summit in Paris a few days earlier, had failed to reiterate the U.S. commitment to Article 5. At every previous summit, it was standard procedure for American presidents to recommit to the article—the ultimate reassurance to allies who felt vulnerable in the face of an aggressive Russia. Such statements, once fundamental to Europeans’ sense of security during the Cold War, may have seemed more pro forma during much of the Bill Clinton and George W. Bush administrations, when relations with a diminished Russia were experiencing a warming trend. But Vladimir Putin’s increasingly aggressive stance and Russia’s invasions of Georgia and Ukraine imbued expressions of U.S. fidelity to Article 5 with renewed urgency and importance.

And yet, Trump choked on the words. Standing, ironically, in front of both a 9/11 and Article 5 memorial at the new NATO headquarters, he spoke, generally, about the allies’ “commitments” to one another, but the missing words loomed larger than the ones he uttered. At the time, it was shocking, but in retrospect, it’s not really surprising. A vigorous internal debate had been raging about whether Trump would restate the commitment. McMaster believed he had prevailed in convincing the President: Senior Administration officials briefed the press as though this were the case. But when it came time to deliver the speech, Trump, following his own instincts, or under the influence of his isolationist adviser Steve Bannon, left out the magic words.

The collective gasps of other NATO heads of state were quickly followed by a sloppy cleanup operation. McMaster told reporters that “of course” Trump clearly meant what he had, in fact, clearly not said. McMaster and Cohn falsely asserted, in their article, that the President had “reconfirm[ed] America’s commitment to NATO and Article 5.” But by the time Trump got around to actually mentioning Article 5, which happened during the visit of the president of Romania to Washington two weeks later, the damage was well and truly done.

From Disdain to Hostility

Things settled down on the NATO front for several months, while Trump pursued North Korean diplomacy and his coveted trade wars. But the twists and turns of 2017 turned out to be nothing but the warm-up act for the high-stakes drama of 2018.

Trump was already in a fighting mood well before the July NATO summit in Brussels. A month earlier, at the G-7 summit in Canada, he had gone out of his way to pick a fight with the United States’s largest trading partners, aiming particular venom on Canadian Prime Minister Justin Trudeau and German Chancellor Angela Merkel. Aides leaked that the tariffs he was already threatening and imposing around the world would be small potatoes compared to what Trump was considering internally: withdrawal from the World Trade Organization. Senior members of the Administration were desperate to get him to climb down off that ledge, aware of the sheer chaos it would inject into the world economy.

But that impulse to withdraw from international institutions and agreements that Trump is convinced treat the United States unfairly soon reasserted itself in the form of grievance against NATO allies.

The ostensible cause of Trump’s ire was the failure of the majority of NATO members to reach the target of committing 2 percent of their GDP to defense spending. This was not, it should be noted, a new concern for the United States. Previous presidents have also been frustrated by other NATO countries’ below-target defense spending; President Obama had previously labeled them “free-riders.” It was, in fact, at the NATO summit in 2014 that Obama reached an agreement for all countries to contribute the 2 percent, which in some cases meant a near doubling of their defense budgets by 2024.

But Trump’s sense of grievance about the unfairness inherent in American guarantees to other countries, crystallized in his obsession with the idea that other NATO members owe the United States “a tremendous amount of money,” overwhelmed all other considerations. He demanded immediate fulfillment of the 2 percent target, threatening to “go it alone” if he did not get immediate satisfaction in this regard. He even floated raising the target to an unreachable 4 percent. Then he abruptly reversed course and chose to claim credit for the vast sums allegedly “beginning to pour in” to NATO coffers.

Trump’s whiplash-inducing claims were exacerbated by his evident confusion about how NATO financing actually works, and his indifference to the broader context. He claimed, inaccurately, that NATO members “owe” the United States money because of their below-target defense budgets. But the 2 percent target applies to NATO member states’ spending on their own militaries, not the more limited funds they pool for shared activities like running NATO’s headquarters and certain common defense structures. The United States is not owed anything. Furthermore, the United States spends a considerable portion of its own defense budget on forces and missions in the Middle East and Asia, which are not a part of NATO’s mandate.

In the end, the NATO summit involved several moments of unpleasantness, including Trump’s public lecturing of the Secretary General, who had actually done his utmost to help Trump take credit for improved finances. But it did not completely fall apart. The Joint Declaration issued by the member states at the summit’s conclusion even included several long-sought provisions intended to strengthen military cooperation. That outcome led Trump’s defenders to assert that fears he would use the summit to announce the United States’s withdrawal from NATO were the result of hysterical media hype.

But were they? Trump takes pride in his own unpredictability, his impulsive, gut-led decision-making that even he cannot predict. But his longstanding antipathy toward alliances in general, and NATO in particular, his performance at the G-7 summit, and his ranting complaints leading up to Brussels led an amazing range of stakeholders to conclude that the danger of withdrawal was real.
One such group was his own staff. Trump’s national security team has a number of quirks and internal incongruities, but devaluing NATO does not feature among them. Secretary of Defense James Mattis, Secretary of State Mike Pompeo, National Security Adviser John Bolton, and White House Chief of Staff John Kelly all hold utterly traditional views about NATO, and have spoken for years about the importance of the bonds and mutual obligations between its members.

But so worried were they that Trump might blow up the summit, that they insisted—and successfully argued to the other member states—on completing the text of the Joint Declaration days before the summit, leaving no final language to be haggled out by the leaders when they rolled into town, as would typically be the case. The risk of leaving anything open to negotiation once Trump arrived at the summit was deemed simply too great. None of these aides wanted to be in the absurd position McMaster and Cohn found themselves in the previous year, twisting themselves into pretzels to claim the President held positions he would not himself articulate.

Another concerned group was Congress. There is not much policy left these days that receives bipartisan consensus on Capitol Hill. But senior members of both parties and of both chambers who specialize in national security have remained strong supporters of NATO, making frequent visits to NATO headquarters and taking interest in its expansion to include new members and new partnerships with other nations. Alarmed by Trump’s attacks on the institution, the Senate moved quickly to pass a resolution reaffirming support for the alliance days before Trump landed in Brussels. The vote was 97-2.

But some felt the need to go further. Under no previous administration has Congress felt the need to put down a marker warning the President not to withdraw from the treaty. But that is exactly what a bipartisan group of senators, led by the late John McCain, Tim Kaine, Cory Gardner, and Jack Reed did on July 26 when they introduced legislation that would prevent the President from withdrawing from the treaty without the Senate’s concurrence. Such legislation, which has not advanced, is constitutionally dubious, but its introduction signaled a genuine fear that Trump might actually carry out his threats.

The third group that genuinely feared Trump might withdraw were our country’s allies themselves. Following his performance at the G-7 summit, in particular, the sense among NATO members was pervasive that if something set off Trump’s temper, his impulsive streak could lead to a catastrophic decision. “The best-case scenario is that it’s just rhetoric,” one delegate said, in what sounded like a desperate attempt to buck up their own spirits.

Again, both before the summit and after it passed without irreversible damage to the alliance, a number of Trump defenders pooh-poohed the idea that Trump would consider withdrawal. But it must be asked: On what basis should observers of his behavior feel confident in that assessment? Because his staff has demonstrated an ability to restrain him on some issues? Sure, except when they haven’t, like when it came to cutting off talks with the British, French, and Germans on strengthening the Iran nuclear deal and instead pulling the United States out of the deal, rather than giving those talks a chance to succeed.

In short, there is little reason to feel confident that Trump would not, at some stage, act on his actual views and respond to his impulses. We may have gotten lucky over the first two years of the Trump presidency, but that is hardly reason to feel sanguine about his decision-making during the next two years.

Trump’s hostility toward NATO, after all, is of a piece with a number of other positions he holds on related issues that make up his foreign policy outlook. He views the European Union with undisguised loathing, considering it a construct that disadvantages the United States in trade negotiations, which he prefers take place on a bilateral basis. So he has cheered on Brexit, lectured British Prime Minister Theresa May on how to drive a hard bargain with the EU, and encouraged French and Italian leaders to reconsider their membership. That he views European unity and integration, long-held American foreign policy goals, as challenges to the United States only reinforces the possibility that he could walk out of NATO.

But perhaps more than on any other issue, it is Trump’s views on Russia that raise questions among allies and NATO supporters about his commitment to the alliance. Possessed of a passionate desire borne of uncertain origins for friendship with Putin, Trump’s solicitousness has clearly emboldened Russia and unnerved Europeans, who believe he is putting their security at risk.

From downplaying Russian election interference to parroting Russian claims about the desires of Crimea’s Russian speakers to be ruled by Moscow to finding excuses not to implement tough new sanctions tools against Putin and his cronies, Trump has sent every conceivable signal that he wants to prioritize warming U.S.-Russian ties while he seeks to cool them with our closest allies. The contrast of his berating of such allies at two consecutive summits with his Putin chumminess in Helsinki, his silence on Russian bullying of those same allies, in addition to the carrying out of chemical weapons attacks in the UK, could not be more jarring, or more illuminating. Imagine what Trump’s performance does to the confidence of, say, the leaders of the Baltic states that the United States will stand with them the next time Russia engages in bullying, or worse.

One of the most damaging aspects of Trump’s ugly rhetoric and unfriendly attitude toward traditional U.S. allies is that he is building up this same hostility toward NATO among his supporters. The President’s ability to reshape long-held attitudes among Republican voters is positively stupefying. Free trade, suspicion of Russia, and a commitment to strengthen alliances have been central pillars of Republican foreign policy for decades, yet after only a few years on the national scene, Trump is bending the party’s positions to his will. Recent polling has been stark, even alarming, in bearing this out. Among Republican voters, and even more so among Trump supporters, backing for tariffs, friendliness toward Putin, and distrust of NATO are on the rise. In one clear example of the trend, a YouGov poll found that in March 2016, Republicans opposed withdrawing from NATO by 48 to 17 percent, whereas in July 2018, views were split at 38 to 38 percent.

That shift threatens to open up a huge breach in the consensus of American support for the alliance that has undergirded Western security for 70 years. And most concerning of all, those attitudes will not disappear when Trump does.

Imagining a World Without NATO

Some have argued that the script of this year’s NATO summit—intense Trump bluster followed by a relatively successful outcome—means that the danger has passed. But they would be wrong. Trump’s anti-NATO sentiment is longstanding and politically expedient. At rallies, Trump whips up the crowd by ticking down his list of punching bags—NAFTA, NATO, Canada (!)—and his followers bay in agreement. As Special Counsel Robert Mueller’s investigation closes in around Trump, he will become even more dependent on his core supporters. Having convinced them to adopt his grievances, as the polling cited previously demonstrates, he will be even more tempted to act on them, demonstrating his defiance to the political establishment and reveling in the cheers of his base. Dismantling the Western alliance to own the libs!

It sounds outrageous, outlandish, literally unbelievable. But it could happen. Trump basks in his willful ignorance of the alliance’s history and strategy and disdains the advice of experts, including those who work for him. He personalizes everything and views all relationships as transactional—the very antithesis of the logic of alliances, in which nations subordinate certain narrow interests in favor of larger common goals. He loves the drama of the kind of outrageous moves that allow him to dominate cable TV coverage, while drawing condemnation from all the right critics. Under the right circumstances, for Trump, pulling out of NATO could be all gain at no cost.

And Trump hasn’t stopped signaling his true feelings about the alliance. During an interview with Tucker Carlson on Fox News days after the NATO summit, he expressed incredulity that the United States might be called to use military force to defend NATO’s newest member, Montenegro, from Russian aggression. Russia has made no secret of its unhappiness with Montenegro’s accession to NATO, and actively backed a coup attempt in 2016 to install a pro-Russian government. So, this is no idle matter. The shivers could be felt not just in the Montenegrin capital of Podgorica, but also in the Baltic capitals of Tallinn, Riga, and Vilnius.

This forces us to confront two difficult questions. The first is, what would it mean if the United States were to withdraw from NATO? It is a stubbornly difficult question to answer, because we honestly cannot begin to imagine living in a new era without these international organizing structures. Because for all of NATO’s challenges, no sane person or American political leader has or would contemplate such a reckless move. And of course, we have done no planning for such a course of action.

But suffice it to say that the implications are innumerable and terrifying. Russia pawing at the Baltics and other Eastern and Central European states is only the most obvious consequence. Western states’ ability to respond to these threats will be hampered by the breakdown of joint defense structures. The absence of a U.S. leadership role in NATO means a less integrated command and control structure, even if the United States were to join European states in common military campaigns.

Without U.S. participation in NATO, the logic of U.S. troops remaining deployed in European bases in Germany, Italy, the UK, Spain, Turkey, and elsewhere quickly breaks down—Trump has already questioned the need for basing forces in Germany—and will be dependent solely on bilateral agreements with host countries. One does not need to be an absolutist unwilling to consider any adjustment in U.S. force structure to understand that a precipitous withdrawal from Europe will result in poorer common European defense capabilities and weaker U.S. power projection to Eurasia when the need arises.

Moreover, one of the most underappreciated benefits of NATO is its success in preventing intra-European conflict. The 70 years since World War II, a period of steadily advancing integration through structures like NATO and the European Union, have lulled many in the West into believing that peace in Europe is a natural, inevitable condition. But a broader view of history quickly tells us otherwise. Centuries of conflict lie beyond the memories of almost everyone alive today, but we would be naïve and unwise to forget them. The NATO umbrella, and the willing submission of European states to U.S. strategic domination, has helped keep those states from turning to military means to settle their own disputes. Crucially, given its history, Germany has embraced a restrained foreign and military policy, dampening one of the greatest internal threats that has plagued Europe in the past. Remove the United States from NATO, and the dominoes could start to tumble. A divided, internally conflicted Europe with the United States on the sidelines could lead to catastrophic humanitarian, security, and economic consequences. Just ask anyone over 85.

But the impact would not be limited to Europe. In the Middle East, where I have focused most of my professional work, all those states that align strategically with the United States would be forced to confront a new reality. Today, Middle Eastern allies of the United States benefit from NATO because of the way it broadens U.S. influence. In a post-NATO world, their alignment would be with an isolated United States that lacks the umbrella of broader Western support.

Israel would be the most severely affected. Israel’s impressive self-defense capabilities will not disappear, but its security partnership with the United States, another critical pillar of its defense policy, will be forced to adapt in complicated ways. The military relationships that animate the partnership day to day are conducted between the Israel Defense Forces (IDF) and U.S. European Command. U.S. forces based in Germany travel to Israel by the thousands to conduct joint exercises, including drills that simulate bringing Patriot missile batteries and other missile defense assets to assist in defending Israel in the case of a major conflict. Other U.S. troops sit even closer, at Incirlik Air Force Base in Eastern Turkey. Remove the United States from NATO—and forward-deployed U.S. forces from Europe—and the United States’s ability to respond to a Middle East crisis would be diminished.

Could U.S. support for Israel be shifted and coordinated instead through U.S. Central Command, based in the Persian Gulf? It has been proposed before as an efficiency measure. But Israeli generals have always resisted the proposal. Their worry is that they would find it challenging to enjoy the same level of intimacy they have today with Europe-based U.S. commanders, with commanders who maintain a similar closeness with Arab militaries. True, Israel is closer strategically today with the Arab Gulf states than at any time in its history, because of a focus on the common threat of Iran and the lower priority of the Palestinian issue. But those relationships are a long way from being normalized and could still backslide. Israeli security planners are, therefore, still most likely to want to maintain separation between their relationships with the U.S. military and with their Arab neighbors.

The Middle East would also experience the effects of NATO’s diminishment in the form of further empowerment of Russia. Already, Russia’s brutally decisive intervention in Syria, combined with successive U.S. administrations’ preference to reduce active U.S. military engagements in the region, have led many regional states to explore expanded security ties with Russia. Israeli Prime Minister Benjamin Netanyahu meets more frequently with Putin than he does with Trump, and the IDF and Russian Air Force deconflict their operations in Syria. The leaders of Egypt, Saudi Arabia, and the United Arab Emirates, all close partners of the United States, have visited Moscow and explored acquiring advanced Russian weapons systems in addition to their American-supplied arsenals. A U.S. withdrawal from NATO, which would unmistakably be understood as a major pullback from the United States’s leadership in global affairs, would turbocharge those trends. The effect of expanding Russia’s influence would be felt far beyond Europe and the Middle East.

Saving NATO

The second, and more urgent, question raised by Trump’s flirtation with this mad idea is: What can be done to prevent it?

The question is difficult to answer in the sense that all questions that rely on predicting Trump’s course of action are. Who could influence him? Which advisers does he listen to, or has he stopped listening to? What arguments would persuade him? And might those intended to persuade actually impel him to do the opposite out of sheer defiance? If he reaches the point where he decides to really take off the shackles—Let Trump Be Trump—proving that he will do the bold (or outrageous) thing no one else would do would be his natural play.

One answer is ensuring that NATO members continue to move smartly toward meeting their commitment to spend 2 percent of GDP on defense. That may sound like the appeasement of a bully, but it is not. It is, in fact, the fulfillment of a promise, pursued by multiple U.S. presidents, and a way to strengthen NATO’s military capabilities. If it allows Trump to claim victory, as NATO Secretary General Jens Stoltenberg has repeatedly encouraged him to do, it may be a bit galling, but it is a small price to pay. Sometimes depriving bullies of excuses is simple prudence.

A second step should be broadening efforts to educate the American public about the value the United States derives from its membership in NATO. The challenge here is that Trump seems most attentive to the core base of his support, whose opinions he has proven to be able to shape as much as he responds to them. Nevertheless, the effort is worthwhile. Stoltenberg took a stab at it during a recent speech at the Heritage Foundation in which he made arguments one could scarcely imagine any previous NATO Secretary General needing to make, as he spoke to NATO’s most basic value to the United States. But Washington think tanks, where a pro-NATO consensus still prevails, may be the least important place to make the argument. A concerted campaign of speeches and interviews in universities, civic organizations, and local media outlets across the nation, by NATO country ambassadors, members of Congress from both parties, and former U.S. military commanders, might have a better chance of shoring up whatever erosion there is in the American public’s support.

But finally, the responsibility of protecting us from an impulsive, historic, and disastrous decision by the President falls to Congress, and particularly to the Republican leadership. Many of Trump’s most controversial policy decisions—withdrawing from the Iran deal and the Paris Climate Accords, or trying to dismantle the Affordable Care Act—are fully consistent with mainstream Republican positions. But when he has challenged Republican orthodoxy by ignoring skyrocketing deficits or, most ominously, in imposing tariffs on trading partners despite longstanding Republican promotion of free trade, the response of congressional leaders has been surpassingly meek. Trump is further emboldened by the utter dereliction of congressional oversight over matters of ethics and basic competent governance.

So it would take a dramatically different reaction from Republican congressional leaders for Trump to understand that withdrawal from NATO is the brightest of red lines. The Senate resolution that preceded the NATO summit is a good start but needs significant reinforcement, both legislatively and rhetorically. Republican leaders must do better than former Speaker Paul Ryan’s weak statement at the time of the summit, in which he called NATO “indispensable” but declined to challenge any of Trump’s bluster. Invitations for Cabinet secretaries like Pompeo and Mattis to testify about NATO’s benefits would help them make those arguments internally. With Democrats now in control of the House, they will have additional opportunities to reinforce support for NATO. But Trump’s position could harden if the issue breaks down along party lines, so strong Republican voices will remain critical.

Finally, we also have to contemplate how an impeachment crisis might be relevant. In such a scenario, where Trump’s fate may lie largely in the hands of Republican senators, the onus will fall on them to make sure Trump understands that NATO is untouchable. They should start using their leverage now.

Essentially, it is all hands on deck. Last July, as Trump brooded and raged about his NATO grievances, we may have been on the verge of a wildly dangerous cascade of events that could have devastated American interests, weakened U.S. leadership, abandoned our allies, emboldened our adversaries, and made the world a darker and more brutal place. No one thinks this is a good idea. But Trump, whose knowledge and values are wanting, whose motivation is suspect, and whose supporters follow him blindly, could have taken us there.

He still could.

So sounding the alarm, maintaining vigilance in defense of a critical component of U.S. national security and world stability, and saying with absolute clarity that NATO withdrawal must be off the table, are the historic responsibilities we must bear until this threat has passed.