Joe Biden has led the national polls in the race for the 2020 Democratic nomination since last year. He's ahead in the first three contests, also, with leads ranging from 7 points (Iowa) to 13 points (New Hampshire) to 28 points (South Carolina). He's first in fivethirtyeight.com's endorsement primary. And though he didn't launch his campaign until the second quarter of 2019, at which point Bernie Sanders had raised the most money, his nonstop fundraising schedule, and great first-24-hours number, suggests that his second-quarter haul will be impressive. Going into tonight's Democratic debate, there was no reason to doubt Biden's status as the Democratic frontrunner. Indeed, while head-to-head matchups 16 months before an election are worthless, one might as well have considered him the frontrunner to become the 46th president of the United States, too.

And yet there is an air of unreality surrounding the Biden campaign, a widespread expectation that the former vice president just can't last. He's run twice before, with terrible results. He's old. He has a tendency to let his mouth take him places his political advisers would rather not have him go. And he has baggage. Lots of baggage, from his creepy-uncle vibe to his votes for NAFTA, the Iraq war, and the 1994 crime bill, to his devotion to the principles of bipartisanship and civility, including with the segregationist and racist senators with whom he has served. He's about as Washington as you can get. There might not be an Acela corridor without him. Alexandria Ocasio-Cortez, for one, is not impressed. "He's not a pragmatic choice," she says.

One of the questions the 2020 Democratic primary will answer, then, is whether the party is more like Biden or AOC. Is a long career, devoted service to Barack Obama, and the purported ability to win the support of working-class whites enough to win the party's nomination? Or have the Democrats moved so left in recent years that Biden's experience is actually a weakness, his geniality a liability, his folksiness a handicap?

The evidence is mixed. Biden's sustained poll position has led some analysts to conclude that, MSNBC and CNN to the contrary notwithstanding, the Democratic Party is older and more moderate than people think. Biden doesn't need to capitulate to Sanders to win the nomination, he doesn't need to apologize to AOC or to Cory Booker. And Biden hasn't apologized, not for his sniffing hair or for his remarks about working with segregationists. And his lead remains significant. Maybe the audience for identity politics and far-left social liberalism is small.

On the other hand, Biden has had to reverse himself on taxpayer funding for abortion, signaling just how essential unrestricted abortion rights have become to the Democratic electorate. And he's wishy-washy on the Trans-Pacific Partnership, which his former boss, the biggest name in Democratic politics, negotiated. Biden's performing a high-wire act, in other words. He has to navigate the shoals of the Great Awokening that has turned the Democratic base, white progressives especially, into zealots for social justice. Up until Thursday, his strategy has been to lay low. Focus on donors. Avoid interviews. Wrestle with Trump, not with the other Democrats.

No longer. He had to stand on stage with nine of his competitors Thursday, and answer questions from Savannah Guthrie, Lester Holt, and Chuck Todd. Next to him was Bernie Sanders, whose "democratic socialism" has determined the contours of intra-Democratic debate since 2016. And next to Bernie was Kamala Harris, the freshman senator from California, who basically defines the idea of "woke capitalism." And next to Harris was Kirsten Gillibrand, who's executed one of the most remarkable political transformations in American history, from middle-of-the-road congresswoman to feminist warrior in a little more than a decade. Also there was Andrew Yang, who wants to give every American a universal basic income. And Pete Buttigieg, the trendy multilingual mayor of South Bend Indiana. And a bunch of other people, including Marianne Williamson, who was visiting from the Age of Aquarius.

And this debate took place a day after Elizabeth Warren and Bill de Blasio called for eliminating private insurance, Julián Castro called for abortion rights for trans men, and Cory Booker and Beto O'Rourke spoke in garbled Spanish. The trend of the Democratic Party is to the left. And it's a trend Biden doesn't seem all that interested in resisting, as evidenced by his joining all of the candidates on stage in calling for health insurance for illegal immigrants. While also saying deportation of illegal immigrants wouldn't be a priority for his administration.

Biden has encountered the Great Awokening, and he doesn't know what to make of it. His instinct seems to be to go with the flow. Maybe you noticed the weird way he responded to questions where the moderators asked the candidates to raise their hands. In each case Biden was tentative, uncertain, looking at the competition. At one point he asked the moderator to repeat a question, highlighting his age.

If you had been dropped into this debate from Mars, you would have thought Kamala "for the people" Harris was the Democratic frontrunner. She brought down the house several times. She got Biden tangled up on the issue of busing. She clearly represents the future of the Democratic Party. She's fourth in the national polls, stuck in single digits. But she went toe to toe with the frontrunner—something that was studiously avoided for most of the two nights of debates. And she won.

Something is happening to the Democratic Party. It's been moving left for years. Since Howard Dean's insurgency in the 2004 campaign, the number of Democrats who have embraced liberalism, progressivism, and now socialism has been steadily increasing. The reason is partly generational. My cohort, the Millennials, embraced the left position on the issues of Iraq and gay marriage, and if anything Generation Z seems to be more left-wing still. The number of liberals is not an overwhelming majority of the party—not according to polls—but it is a majority. And the number of lefties is so great that it determines the nature of the interest groups that dictate the party's agenda and talking points. It might even determine the nominee.

And if that's the case, simply judging by his performance on Thursday night, Joe Biden has got to be awfully worried.