Does Donald Trump have a foreign policy?

During the transition period alone, the President: broke decades of tradition and talked to the President of Taiwan; condemned China for seizing a U.S. underwater drone in the South China Sea, then reversed his view the same day with a tweet telling China to “keep it!”; took the side of Russian President Vladimir Putin after President Obama sanctioned Russia for interfering in the U.S. presidential election.

Trying to piece Mr. Trump’s foreign policy together, one cannot be blamed for missing the grand strategy in it all.

Maybe Trump is a realist; or maybe he wants to dismantle the U.S.-led international order. Perhaps he is purely a dealmaker.

Whatever the approach, one theme is consistent in Mr. Trump’s actions and words: his desire to make U.S. foreign policy appear as unpredictable as possible. As Trump so succinctly summarized it himself during a foreign policy speech in April 2016: “We have to be unpredictable.” Call it a “doctrine of unpredictability,” if you like.

Donald Trump believes that the United States should pursue the foreign policy of a gambler, shedding the more “predictable” aspects of U.S. foreign policy that have, until now, helped keep the world somewhat stable. As gambler-in-chief, Trump’s perceived unpredictability will supposedly give him leverage to negotiate anything with anyone at anytime.

The idea might not seem so ridiculous at first blush—after all, a good poker face is an important part of success when staring down opponents.

But foreign policy isn’t a poker room at a Trump casino. The only thing that a doctrine of unpredictability is really sure to do is gamble with U.S. national security—shattering U.S. alliances, destabilizing relationships with adversaries, and suppressing public debate in the United States.

For decades, American leadership has rested on a complex web of alliances and partnerships that create stability through predictability around the world. Peace and prosperity in international affairs rely on agreements between nations—whether security alliances, trade agreements, or otherwise—and the ability of nations to trust that partners will follow through on those commitments.

For example, knowing that members of the World Trade Organization can be penalized economically for breaking trade rules helps keep the international economic playing field from devolving into a series of trade wars. Knowing that countries will respond fiercely to violations of sovereign borders—such as Iraq invading Kuwait or Russia invading Ukraine—helps keep the peace. While these rules are not always enforced, they provide a strong deterrent to potential bad actors.

Crafting a foreign policy of unpredictability, Mr. Trump believes, would give the United States the upper hand in its dealings around the world. Mr. Trump sees international agreements and alliances as stifling to American action, rather than as force multipliers for American leadership. He acts as though the United States can get what it wants on its own terms, by itself, no matter what the issue. This strategy is premised on the notion that friends and enemies alike should not know what the United States would do in any given situation. As Trump once put it: “I don’t want them to know what I’m thinking.”

This is a terrifying prospect for those around the world who rely on American leadership to underwrite global peace and prosperity.

In 1962, former U.S. Secretary of State Dean Acheson was dispatched to brief French President Charles de Gaulle on the Cuban Missile Crisis and enlist French support. When de Gaulle was offered evidence to verify the briefing, de Gaulle reportedly waved off the offer, making clear that he trusted the United States. Mr. Trump’s approach would undoubtedly destroy this kind of trust in U.S. leadership going forward.

His foreign policy of unpredictability would mean raising questions about U.S. commitments to allies from Europe to Asia. When asked about U.S. alliances with Japan and South Korea, Mr. Trump said “there is going to be a point at which we just can’t do this anymore.” When asked about NATO, his sarcastic response made it clear that he believes that the U.S. is committed to too many alliances: “[W]e defend everybody. When in doubt, come to the United States. We’ll defend you.”

The dangers here are manifold. Undercutting U.S. alliances emboldens adversaries to test those alliances, weakening regional stability in places like Europe and Asia where Russia and China are already worrying neighbors. And while Mr. Trump believes he can squeeze more money from U.S. allies in an approach reminiscent of a protection racket rather than an alliance, those allies may very well come to believe they too can get better deals elsewhere. Apparently Mr. Trump is comfortable with this, as was evident from his willingness to see other countries in Northeast Asia acquire nuclear weapons.

The consequences of this scenario could deal a blow to U.S. national security interests. The deeply destabilizing effect the absence of U.S. alliances would have on Northeast Asia, for instance—weakening deterrence against North Korea, raising the possibilities of a Japan-China clash, and the economic ramifications of regional conflict—would be devastating. Likewise, a NATO without a reliable U.S. ally—on top of Russian aggression, Brexit, the refugee crisis, and the right-wing trend in European politics—could be the straw that breaks Europe’s back.

The same risks go for the global economy. Donald Trump regularly trots out his business experience as a supposed asset that would enable him to negotiate better deals on everything from alliance treaties to trade deals. But business deals are not global politics. Mr. Trump’s threat to use trade as a stick in negotiations could have a deeply worrisome effect on global economics. Trade agreements provide predictability upon which businesses, consumers, and governments are able to make decisions about where to invest. A U.S. President willing to rip up U.S. trade commitments at any moment may end up scaring markets and potential partners who fear America’s unreliability. In the end, all of this would hurt the pocketbooks of Americans.

And how would this  doctrine of unpredictability play out in dealing with adversaries?

Much has been written about how Mr. Trump’s desire for unpredictability is akin to what President Richard Nixon reportedly referred to as his “Madman Theory.” In 1968, Nixon told his advisor H.R. Haldeman that “I want the North Vietnamese to believe I’ve reached the point where I might do anything to stop the war.” Later, in 1969, consistent with the Madman Theory, Nixon raised military alert levels in what some analysts believe was an attempt to rattle the Soviet and North Vietnamese leaders.

While some amount of unpredictability is indeed necessary when dealing with adversaries, too much ambiguity can be destabilizing. Mr. Trump’s policy statements to date don’t leave others wondering how far he’ll go—they leave everyone wondering what his basic policy is. For instance, Mr. Trump has signaled wildly different instincts on how he would deter Chinese assertiveness in the South China Sea. In a Washington Post interview Trump stated “I don’t think we are going to start World War III over what they did…”, while in a New York Times interview he said, “Look, would I go to war? There’s a question I wouldn’t want to answer.”

Mr. Trump’s foray into the Taiwan issue at the end of 2016 is a perfect example of the dangers of unpredictability. While Mr. Trump did not appear to be aware of the massive shift in policy he was signaling by taking a call from the president of Taiwan, he doubled down on that policy shift by then questioning the One China policy that underpins U.S.-China relations. Mr. Trump and his team have spun this as a way to gain leverage with China, but it’s unlikely China will be willing to play that game with sovereignty issues like Taiwan or the South China Sea.

It seems much more likely that adversaries would interpret this foreign policy of unpredictability as malleable, rudderless, and unprincipled, something they can take advantage of rather than something to be feared.

This would undermine the very foundation of deterrence—that countries make clear what they are willing to do to defend their interests. For instance, for decades Russia has known that if it were to invade a NATO ally, the United States would come to NATO’s defense. But if a country’s policy becomes murkier, it could invite aggression to test those policies—and that’s how wars start.

This weakness would be exacerbated by a perception that Mr. Trump does not have a firm grasp of foreign policy—and that a foreign policy of unpredictability is a good way to hide this fact. During the campaign, even Senate Majority Leader Republican Mitch McConnell said of Trump, “it’s pretty obvious he doesn’t know a lot about the issues.” Whether it’s the One China policy, nuclear weapons, or the difference between Hamas and Hezbollah, reading Mr. Trump’s tweets and listening to his statements make it hard to believe that he has a firm grasp of any top foreign policy issues. His use of “unpredictability” as a mask for his ignorance can only last until world events and the need for a real-time U.S. response reveal otherwise.

There’s a crucial difference between employing the Madman Theory and being an actual madman.

Mr. Trump’s doctrine of unpredictability will also have consequences domestically. Using unpredictability as a pretext is a way for Mr. Trump to continue hiding information that the public normally expects. (During the campaign, Mr. Trump did not release his tax returns or complete health records, for example.) When applied to foreign policy, this lack of transparency could stifle a true public debate on serious policy issues.

The conduct of foreign policy is inherently a more opaque endeavor than domestic policy, mostly because dealing with foreign governments requires a degree of secrecy to maintain leverage. But over the history of the republic, the United States has developed strong mechanisms to ensure that there is a robust public debate over national security policy: daily press briefings at the White House and State Department, oversight committees in Congress, and use of the media, to name a few.

When talking with the media Mr. Trump has used the unpredictability excuse numerous times to evade answering foreign policy questions. If this continues as the Trump Administration’s public approach, unpredictability could become a guise for withholding information from the American people.

And attempting to shut down public debate on key foreign policy issues would enable a dangerous expansion of the President’s power to conduct foreign policy without oversight. The aftermath of Richard Nixon’s presidency—including the Church Committee investigations that revealed tremendous executive overreach and violations of the law—made very clear the perils of a President and an executive branch that doesn’t believe in transparency in the conduct of foreign policy.

This penchant for secrecy is part of Mr. Trump’s general refusal to believe that he is (or should be) subject to public scrutiny—whether it’s his criticism of the media or unwillingness to divest from his business ties. As Mr. Trump put it at the Republican National Convention: “I alone can fix it.” The message to everyone is: “Trust me. Don’t sweat the details.”

In foreign policy, every American should demand predictability—and transparency—from the President. U.S. national security depends on it.