Former Vice President Joe Biden speaks during the House Democrats retreat on Capitol Hill in February.Eric Thayer / Reuters

There are plenty of reasons to downplay the ideological significance of 28-year-old Alexandria Ocasio-Cortez’s upset win yesterday over House Democratic powerbroker Joseph Crowley. Even by the standards of congressional primaries, turnout was low. In a district of roughly 650,000 people, Ocasio-Cortez won with only 16,000 votes. Ocasio-Cortez’s victory can also be chalked up to ethnic succession. Crowley is an Irish American representing a district, in Queens and the Bronx, that was once filled with white ethnics. Today it is less than 20 percent white and almost 50 percent Latino. Ocasio-Cortez exploited that shift by emphasizing her Puerto Rican roots. Finally, Ocasio-Cortez is a woman running in a year in which the #MeToo movement and the backlash against President Trump has palpably boosted Democratic women candidates.

If these were the only explanations for Ocasio-Cortez’s victory, it wouldn’t herald much about the ideological direction of the Democratic Party. But Ocasio-Cortez’s upset isn’t only a story of generational, ethnic, and gender succession. It’s also a story of ideological succession. And if I were former Vice President Joe Biden mulling a presidential bid in 2020, that would worry me a great deal.

Since he entered the House in 1999, Joseph Crowley has always stayed in his party’s ideological mainstream. But that mainstream was once much more conservative than it is today. Crowley’s a Catholic. And like many Catholic Democrats in the 1990s and 2000s, he sought a middle ground on abortion. While supporting abortion rights, he in 2000 and 2003 backed legislation to ban the procedure dubbed “partial-birth” abortion. He sought a middle ground on the economy too. Crowley was no Ted Cruz: He opposed George W. Bush’s 2001 tax cuts. But like many Clinton-era Democrats, he sought to prove that Democrats were not anti-business or anti-Wall Street. In 1999, he voted to overturn the 1933 Glass Steagall Act, which restricted the activities of banks. In 2002, he earned a lukewarm 78 percent rating from the AFL-CIO. In the wake of 9/11, when many Democrats feared being caught on the wrong side of the nation’s surging jingoism, Crowley embraced hawkish stands that slighted civil liberties. He backed a constitutional amendment banning flag burning. He supported the Patriot Act. He voted for the Iraq War.

At the time, none of this made Crowley an ideological outlier. Many nationally ambitious Democrats—from Bill Clinton to Hillary Clinton to Al Gore to John Kerry to Richard Gephardt—took similar stances. Their centrism stemmed partly from ideological conviction. (Many Democrats worried that excessive regulation had contributed to the economic stagnation of the Carter years. Many had grown more hawkish as the result of America’s military victories in the Gulf War and the Balkans in the 1990s). And their centrism stemmed partly from fear of right-wing attacks and the need to raise money from big business and Wall Street. Like many of his party’s leaders, Crowley was a “New Democrat.” Indeed, for four years he chaired the New Democrat Coalition in Congress.

But in recent years, the New Democratic wing of the Democratic Party has withered. And in response, Crowley has shifted left to stay in his party’s mainstream. After initially supporting legislation to weaken the Dodd-Frank restrictions on Wall Street, in 2015 he came out against it. After initially praising the Trans-Pacific Partnership (TPP), he turned against it too.

Other Democrats have followed a similar path. John Kerry, who also voted to authorize the Iraq War, voted against funding it while facing a fierce anti-war challenge in the 2004 Democratic primaries from Howard Dean. After losing to Barack Obama in 2008 in part because of her vote for the Iraq War, Hillary Clinton apologized for it in the run-up to her 2016 presidential bid. She also reversed her prior support for TPP and dramatically distanced herself from her husband’s punitive anti-crime policies.

The problem for Crowley, like Kerry and Clinton, was that their newfound progressivism didn’t appear genuine. Although they now checked the boxes as stalwart progressives, their prior careers as New Democrats made them suspect to a party base hungry for authenticity and courage. Which helps explain why Kerry almost lost to Dean in 2004, why Obama beat Clinton in 2008, and why Clinton faced such a formidable challenge from Bernie Sanders in 2016.

That’s why Ocasio-Cortez’s victory isn’t sui generis. It’s part of a broader pattern that has been playing itself out in Democratic primaries for more than a decade. And it could spell trouble for the man some in the media consider the Democratic frontrunner in 2020: Joe Biden.

The former senator and vice president’s career follows an arc similar to Crowley’s. For much of his time in Congress, he was a New Democrat. A devout Catholic, he once sought a middle path on abortion: supporting abortion rights but opposing government funding of it. He supported NAFTA. He backed the Iraq War and didn’t only vote for the Patriot Act but boasted about writing it.

In recent years, like Crowley, he has shifted left. He’s said he regrets voting to repeal Glass-Steagall. He’s announced that, “I used to be a free trader, but have moved to being a fair trader.” And he’s apologized for the Senate Judiciary  Committee’s treatment of Anita Hill during the 1991 Clarence Thomas confirmation hearings, during which Hill testified that Thomas sexually harassed her. Biden was chair of the committee at the time.

If Biden runs in 2020, these old views will dog him. He’s likely to face younger Democrats who, like Ocasio-Cortez, entered politics after the New Democratic era had ended, and older ones, like Bernie Sanders, who rejected it all along. And he’ll do so in an era in which, more than at any time since the early 1970s, the activist left is defining the Democratic Party.

In retrospect, one of the most striking features of the 2016 primaries was that Hillary Clinton didn’t really attack Bernie Sanders for being a socialist. She rarely parried his attacks on her husband’s polices on crime and Wall Street. She spent more time trying to get to his left on gun control. For Clinton, for Crowley, and for Biden, the New Democratic ideology that they once proudly espoused has become a source of shame. And when you run for office ashamed of principles that animated much of your career, you’re vulnerable to people who aren’t.

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