This article originally appeared in The Guardian on October 22, 2019.

Two years ago, Alexandria Ocasio-Cortez was a bartender and waitress who was generally unknown outside of New York City progressive activist circles. Today, as the Democratic US representative for New York’s 14th congressional district, she is the youngest woman ever elected to Congress and one of the most famous politicians in the country. Celebrity is a major currency of power in American politics, so it was a big deal that over the weekend AOC (as she often is referred to) officially endorsed the Vermont senator Bernie Sanders for her party’s presidential nomination rather than Elizabeth Warren, senator from Massachusetts. This endorsement may in fact have a critical impact on the presidential race, although not in the way that most media outlets are predicting.

Representative Ocasio-Cortez became famous in part because so many conservatives hate her passionately. As a young, attractive, democratic socialist woman of color, she was tailor-made to become an unhealthy obsession for President Trump and his supporters. She was a prime target of Trump’s infamous “go back” tweet, and even amid the current uproar over impeachment, rightwing media have tried to create a scandal over how much she recently paid for a haircut. But the vitriol from the right is countered by adoration from the political left, thanks not only to Ocasio-Cortez’s 5.6 million Twitter followers but to her introduction of the Green New Deal, a hugely ambitious (and expensive) climate-and-jobs program. It’s a sign of her outsized influence that nearly all of the Democratic presidential candidates (including former vice-president Joe Biden) have endorsed the Green New Deal, at least in broad outline.

Ocasio-Cortez has come to embody the Democratic party’s movement toward the left and the growing impact of young people, women and minorities. Both Sanders and Warren, as the leading progressive candidates, clearly coveted her endorsement. Warren had for several months been drawing support away from Sanders, especially among his core base of young voters, even before his heart attack threatened to further depress his polling numbers. So when Ocasio-Cortez called Sanders in his hospital room and told him that she would endorse him, it was an adrenaline shot for his campaign – the ultimate political get-well card.

Some have criticized Ocasio-Cortez for supporting the oldest white guy in the race rather than a woman or minority candidate. But she worked as an organizer for Sanders’ 2016 presidential campaign, and organizations formed by former Sanders staffers and supporters recruited her to run for Congress. Ocasio-Cortez is a member of the Sanders-supporting Democratic Socialists of America, an anti-capitalist organization that works within yet stands apart from the Democratic party. Ocasio-Cortez’s Green New Deal is essentially a compendium of policy goals drawn from the DSA platform.

To the untrained eye, there might appear to be little difference between the policy positions Sanders and Warren have put forward in this campaign. Both support the Green New Deal, Medicare for All and a single-payer healthcare system, student loan forgiveness, free public college, a wealth tax on the super-rich, universal childcare and early childhood education. Sanders has recently followed Warren’s lead in calling for breaking up big tech companies such as Google and Facebook. The numbers attached to his climate change and affordable housing plans are bigger than Warren’s, but that’s a difference in degree not kind.

But Sanders, unlike Warren, declares that he’s leading a revolution. As Ocasio-Cortez told an interviewer after making her endorsement public, the Sanders effort is “far larger than a presidential campaign. This is really about creating a mass movement, a multiracial mass movement of working-class Americans” to achieve Sanders’ policy goals. Further, Sanders has said that he wants to overthrow the capitalist system, while Warren has called herself a believer in markets who is a “capitalist to my bones”.

It’s far from clear how the revolution Ocasio-Cortez describes would stand up to the power structure and sustain itself outside of Sanders’ presidential campaign. It’s also unclear how Sanders’ democratic socialism differs from garden-variety social democracy, since he hasn’t said what sectors of the economy (other than the health insurance industry) he wants to nationalize. Claiming to be a socialist revolutionary may be no more than a way for Sanders and his supporters to assert that their programs are superior to similar programs advanced by non-socialists. In the words of Saikat Chakrabarti, a former Sanders campaign official and Ocasio-Cortez’s first chief of staff, “The real divide is not between left and right. It’s between ambition and not ambition.” Non-revolutionary policies, according to this logic, can be dismissed as unambitious.

Although Ocasio-Cortez’s endorsement undoubtedly will energize Sanders’ campaign, it remains to be seen if her involvement will broaden its base or boost Sanders to frontrunner status. There’s considerable overlap between her supporters and his at the national level, and Ocasio-Cortez may not do much to influence those minority voters the Sanders campaign has struggled to attract. It’s suggestive that Representative Ayanna Pressley of Massachusetts, who is African American, has been the only member of Ocasio-Cortez’s “Squad” of progressive first-term congresswomen who has not endorsed Sanders’ campaign.

But the most significant impact of the Ocasio-Cortez endorsement may be that it gives the Sanders campaign sufficient momentum to carry on deep into the primaries. If that proves to be the case, Warren will have to continue to try to outflank Sanders on the left in order to dominate the progressive lane. Ocasio-Cortez may see this as the best outcome: if Warren were to edge out Sanders for the nomination, she at any rate would be inextricably committed to far-left positions.

But there’s a real danger, under this scenario, that if Warren were to go too far left during her pursuit of the nomination, she would find it very difficult to pivot toward the center to pick up the support of at least some moderates in battleground states like Michigan and Wisconsin, which she would have to have in order to win a tight race against Trump. Progressive ideologues may howl that such political calculations amount to defeatism of the vilest sort, but Mitt Romney experienced precisely this problem when he was forced too far right in the 2012 Republican primaries, which was a critical reason why he lost to Barack Obama in the general election. Ocasio-Cortez may have reason to reflect on the old truism that the best can be the enemy of the good.

This article was amended on 23 October 2019 because an earlier version incorrectly referred to Warren as the frontrunner for the Democratic party presidential nomination. At the time of writing Joe Biden holds that position.

Geoffrey Kabaservice is the director of political studies at the Niskanen Center in Washington DC as well as the author of Rule and Ruin: The Downfall of Moderation and the Destruction of the Republican Party.