The conventional wisdom is that Bernie Sanders is a victim of his own success. His “populist agenda has helped push the party to the left,” declared The New York Times in its story about his presidential announcement. But in 2020, he may lose “ground to newer faces who have adopted many of his ideas.”

There’s an obvious truth here: From a $15 national minimum wage to Medicare for all to free college tuition, Sanders’s opponents have embraced policies that were considered radical when he first proposed them during the 2016 campaign. But what the Times misses is that there’s another policy realm where Sanders may find it easier to carve out a distinctly lefty niche: America’s relationship to the rest of the world.

In 2016, foreign policy was the area where Sanders distinguished himself least. For the first five months of his candidacy, his campaign website didn’t even include a foreign-policy section. At a debate on November 14, 2015, when the moderator, John Dickerson, asked Sanders about the ISIS attacks that had killed more than 100 people in France the previous day, the Vermont senator dispatched the subject in a mere two sentences and then pivoted to domestic affairs.

This time, by contrast, Sanders arguably talks about foreign policy more than any other declared candidate does. Of the four senators who launched their candidacies via video—Elizabeth Warren, Cory Booker, Kamala Harris, and Sanders—only his mentioned foreign policy. Over the past two years, Sanders has given two speeches outlining a broad foreign-policy vision. (Warren has delivered one, last November at American University, which she paired with an essay in Foreign Affairs. Booker, Harris, Amy Klobuchar, and Kirsten Gillibrand haven’t given any.) And of the senators running for president, Sanders owns the biggest foreign-policy victory of the last Congress: the vote to end U.S. funding for the Saudi war in Yemen.

Peter Beinart: What the Yemen vote reveals about the Democratic party

But Sanders doesn’t just talk about foreign policy more. He talks about it in a more radical way. None of the senators running for president are hawks. Last January, Booker co-wrote an op-ed arguing that—absent new congressional authorization—it would be illegal to keep American troops in Syria once the fight against ISIS was over. In her Foreign Affairs essay, Warren called for “ending” the “endless war” that has “sapped” America’s “strength,” and for rethinking the “singular focus on counterterrorism” that “has dangerously distorted U.S. policies.” Warren and Gillibrand also led the fight to keep the Trump administration from pulling out of the Intermediate-Range Nuclear Forces Treaty with Russia.

What distinguishes Sanders is the same quality that distinguished him on domestic policy in 2016: his willingness to cross red lines that have long defined the boundaries of acceptable opinion. One clear example is Israel. Most of the Senate Democrats running for president have shifted left on the subject. Booker, after initially supporting legislation to criminalize boycotts of the Jewish state, voted against a similar bill last month. Warren, after defending Israeli military actions in the Gaza Strip earlier in her career, last year criticized Israel’s response to protests there. But Sanders has gone much further: He’s produced videos that call Gaza an “open-air prison,” he’s depicted Benjamin Netanyahu as part of the “growing worldwide movement toward authoritarianism,” and, most controversially of all, he’s suggested cutting U.S. military aid to Israel.

But Israel is only the beginning of Sanders’s sacrilege. He’s the only presidential candidate in recent memory who regularly describes the Cold War not as a heroic American victory, but as a cautionary tale. Sanders doesn’t just warn against U.S. military intervention in Venezuela, as Warren and Gillibrand have. He warns against it while invoking the United States’ “long history of inappropriately intervening in Latin American countries.” In his speech at Westminster College in 2017, he spent paragraph after paragraph detailing America’s disastrous 20th-century interventions: Iran, Chile, El Salvador, Guatemala, Vietnam—a litany that resembled a Noam Chomsky lecture more than a typical presidential candidate’s foreign-policy speech.

Peter Beinart: America needs an entirely new foreign policy for the Trump age

Sanders’s darker view of Cold War foreign policy isn’t mere historical revisionism. It’s linked to his critique of American foreign policy today. Now, as then, he wants America to shun the quest for global supremacy that leads it to overthrow regimes it can’t control and to instead pursue a foreign policy based on “partnership, rather than dominance.” That’s why, in his Westminster speech, Sanders did something Democrats have rarely done in recent decades: He called for putting the United Nations—which he called “one of the most important organizations for promoting a vision of a different world”—near the heart of American foreign policy.

What all this represents is a second phase of the assault on American exceptionalism that Sanders launched in 2016. Back then, Sanders challenged the domestic side of the exceptionalist creed: the belief that American capitalism—buttressed by modest regulations and welfare provisions—provides upward mobility. Now Sanders is poised to challenge exceptionalism in foreign policy: the belief that America, as a uniquely virtuous nation, can substitute its own self-interest and moral intuition for international institutions and international law. Once again, Sanders’s heresies mirror the anti-exceptionalist turn among America’s young. A 2017 Pew Research poll found that Americans over the age of 30 were far more likely to say that the “U.S. stands above all other countries in the world” than to say, “There are other countries that are better than the U.S.” But among adults under 30, the latter view predominated by a margin of more than two to one.

Sanders’s foreign-policy radicalism may not reshape the Democratic Party as dramatically in 2020 as his domestic-policy radicalism did in 2016, because foreign policy simply doesn’t matter as much in contemporary politics as does domestic policy. But it may offer Sanders a way to distinguish himself among a field that, on domestic policy, is ideologically bunched together. For a presidential candidate, challenging American exceptionalism would, until recently, have seemed like a sure path to political oblivion. In a general election, it still might be. Sanders’s critique of America’s past sins could leave him vulnerable to Republicans who accuse him of “blaming America first.” And his emphasis on international cooperation and international institutions may seem naive when applied to zero-sum great power conflicts in places such as the South China Sea.

Still, Sanders is poised to once again widen the parameters of acceptable debate. In 2016, he found a surprising appetite for his anti-capitalist heresies among the progressive young. In 2020, Americans will learn whether there’s a market for his anti-imperial heresies too.