If, as looks increasingly likely, Joe Biden decides to enter the Democratic primary, the person most responsible may well be Bernie Sanders—who has done more than anyone else to puncture the impression of inevitability that discouraged prominent Democrats from challenging Hillary Clinton. No longer easily dismissed as an eccentric long shot, Sanders has forced an intra-party debate on ideology, tactics, and the relationship between left-wing activists and the Democratic Party mainstream. This debate—taking place in the pages of journals like Dissent and The American Prospect—reflects thoughtful engagement with the changes occurring within the Democratic Party, whose agenda is increasingly shaped by left-wing activists. (As Ryan Lizza recently noted, compare Sanders’s rise to the changing fortunes of a figure like Jim Webb.) Dissent’s and the Prospect’s pieces focus, respectively, on the activist “amateur” left and on the presidency. They make cogent observations about the changing face of progressive politics in America. But they should be read with caution: if too much emphasis is placed on activism, or on the Sanders phenomenon, the left risks perpetuating a mindset that results in misinterpreting political dynamics and misallocating attention. Amateur activism and the presidency are undoubtedly crucial—but brutal legislative realities must also feature in any analysis of American liberalism’s near future.

Sanders’s popularity owes much to the palpable exasperation he so unapologetically conveys, and which fits well with the disappointment of some Obama-era liberals. Sanders openly denounces the post-Citizens United election process as corrupt. His frank, abrasive demeanor conveys neither Clintonian calculation nor that almost-too-serene Obama-style detachment. More than any other candidate, he embodies the tension between the Democratic Party’s activist and establishment wings, and his success has inspired widespread reflection about the relationship, on the left, between these wings.

One of these reflections appears in the new issue of Dissent, where David Marcus—in an article which doesn’t mention Sanders by name, but which is accompanied by a picture of him—praises “amateur politics,” arguing that “the left’s strength, and its power, will always lie outside formal politics.” The outsider status of leftism enables activists to “demand what appears to be impossible to those within; our acts of organized dissent—our pressure and publicity campaigns—can insist on a set of political alternatives.” The implication is that those alternatives can find their way into mainstream political debate, if only they are provided the right channel.

That implication is made explicit by Harold Meyerson in the American Prospect, who argues that Sanders’s ‘revolutionary’ agenda has a symbiotic relationship to Clinton’s ‘progressive’ one. If Sanders needs Clintonian political power to realize his goals, then Clinton needs Sanders-esque agitation to push slow-moving institutions to accomplish liberal goals. “The great bursts of progressive reform in the 1930s and 1960s were the joint product of liberal presidents and turmoil in the streets—general strikes in the ’30s, civil rights protests in the ’60s,” Meyerson writes. “In the United States, liberalism advances only when radicalism is bubbling, which is why Clinton and Sanders need each other, and why the Democrats need them both.”

This is a fitting synthesis for left-wing voters whose ideological sympathies lie with Sanders, but whose pragmatic instincts incline towards Clinton. For them, the dynamic described by Meyerson is a win-win: Even if Sanders fails in getting the nomination, he’s changed the agenda of the Democratic primary, bringing to the fore issues that the more cautious Clinton campaign might have ignored. This is not only psychologically comforting; it’s a largely apt description of liberalism’s 20th-century history and its current political dynamics. And it’s healthy for liberals, whose ideological and tactical divisions on these issues are generally accompanied by mutual suspicion, to think about how such tensions could be directed productively towards progressive reform—instead of descending into internecine sniping that ultimately benefits the right. After all, left-wing energy in recent years has often been concentrated in movements with no formal relationship to the Democratic Party, like the DREAM protesters, Occupy Wall Street, and Black Lives Matter. As Marcus writes, “we are witnessing an exciting uptick in citizen insurgencies,” as Americans direct “more and more of their energies to sites of political action outside formal institutions of power.” The potential latent in this development—progress on immigration reform, economic inequality, racial justice, and much else—will require a sharper understanding of the relationship between institutionalized powers and activist movements, as well as a certain degree of trust.

These analyses capture much of what is distinctive about progressive politics in America in 2015, but they should be applied to the Sanders-Clinton competition only with care and caution. Marcus’s piece praises the insurgent efforts of the “amateur” left, and Meyerson’s proposes that this insurgent agenda, if adopted by Sanders, could advance in moderated form the similar goals of American liberals. Both views, in this sense, offer an account of left-wing progress—either by a Sanders campaign that wins the nomination, or else by one that succeeds in pushing the victorious candidate leftward.

The problem, however, is that the next Democratic president is unlikely to make serious progress on most of the reforms favored by activist groups, for the same reason that President Obama hasn’t: The Democrats almost certainly won’t control Congress. The recent focus on Bernie vs. Hillary risks overlooking this one structural factor that is vastly more important than the identity of the Democratic nominee. Jamelle Bouie made a version of this point in a recent piece, and it bears repeating. Not only the prospect of progressive change, but the ultimate content of that change, is largely up to factors beyond the control of the president. This was the stubborn fact that explained why some of Obama’s reforms were not more progressive, and why other priorities never got off the ground. As Bouie insists: “We can criticize Obama for everything he didn’t do as a legislative leader, but the truth is that his plans were steered, in large part, by the right flank of the Democratic Party,” Bouie writes. The same thing would be true of President Sanders.

Actually, it would be more accurate to say that the same would be true under the best of circumstances: Sanders’s ambitions would be limited by the right flank of the Democratic Party if Democrats held the House and the Senate. But that’s pretty unlikely. Retaking the Senate in 2016 will be difficult; retaking the House even more so. Last year, one analyst predicted that if Hillary Clinton won, she would be the first Democratic president in the history of the party to never once hold the House. Under those circumstances, no ambitious agenda of progressive reform is going to be passed, regardless of the dynamics between activists and the Democratic Party, or the influence of Sanders on Clinton, or the ultimate victor in the Democratic primary.

The most likely outcome of a Democratic presidential victory in 2016 is an agenda that achieves less than President Obama has, since the next president will likely have no similar period during which Democrats control both the White House and Congress. The most important accomplishment possible under such conditions is likely to be essentially conservative: preserving the steps taken by Obama, extending them where possible, and preventing serious rollback by Congressional Republicans. The president has powers in other areas, of course—agency appointments, executive actions, and the considerably greater leeway available in foreign policy. But when it comes to a lasting domestic agenda, the Democrats’ disadvantage in Congress may mean that a Sanders administration is less different from a Clinton administration than their campaigns might suggest. If the GOP succeeds in sharply limiting reforms under the next president, activists (and a number of mainstream Democrats) will justly be left wanting more, but their disappointment will have little to do with whoever wins the nomination. That should be a sobering fact for liberals—which is why Democrats are starting to pour more resources into state-level politics. They should similarly guard against the seductive assumption that landing on the right presidential candidate will get the job done.