Like the Ireland that William Butler Yeats wrote about in his poem “Easter, 1916,” the Democratic primary is “changed, changed utterly.” This time last week, Joe Biden looked like a dead man walking. A day after Super Tuesday, he now leads Bernie Sanders, the erstwhile front-runner, in the delegate count, and the online prediction sites are giving him a roughly seventy-five-per-cent chance of getting the nomination.

How did this sudden transformation come about? One theory we can dismiss right away is that Biden himself was responsible. He gave a powerful and emotive speech in South Carolina, on Saturday, after his big victory there. But when he appeared in Los Angeles, on Tuesday night, he was the same unsteady performer we have seen many times before. He shouted rather than spoke; he momentarily mixed up his wife and sister. His speech didn’t really go anywhere.

Another explanation, which has more substance to it, is that the traditional Democratic power structure, aghast at the prospect of a Sanders candidacy, conspired to deny him the knockout victory that he appeared to be heading for on Tuesday. This theory is popular among Sanders supporters, of course, and it also has an adherent in the White House. “The Democrat establishment came together and crushed Bernie Sanders, AGAIN,” Donald Trump tweeted on Wednesday morning.

Many established Democratic politicians did line up behind Biden. James Clyburn, the Majority Whip in the House of Representatives, started the process with the endorsement he issued in Charleston, South Carolina, last Wednesday. (Clyburn “literally saved the Democratic Party,” James Carville, the veteran Democratic consultant, commented on Tuesday night.) In the days before Super Tuesday, when Pete Buttigieg and Amy Klobuchar both dropped out of the race and endorsed Biden, their gesture seemed to be timed to give him additional momentum as voters headed to the polls, and to blunt the momentum of Sanders. It looks as if the exits and endorsements had a big impact. Take Biden’s victory in Klobuchar’s home state of Minnesota. Until last weekend, he had been polling in the single digits there.

The problem with the party-establishment theory isn’t that it lacks factual basis. It’s that it robs Democratic voters of agency and understates the overarching factor in this year’s primary—fear of Trump getting a second term. In my experience, most ordinary Democrats are so eager (desperate might be a better word) to get Trump out of the White House that they would vote for practically anybody whom they adjudge to have the best chance of beating him. For months, Democrats had been anguishing that the primary had turned into a circular firing squad. When the choice before them was finally reduced to manageable proportions, a plurality of Super Tuesday voters plumped for Biden over Sanders, Michael Bloomberg, Elizabeth Warren, and Tulsi Gabbard. That decision was theirs: it wasn’t made for them by Nancy Pelosi or Tom Perez or CNN.

The influence that Trump exerted was evident in the answers that Democratic voters gave in exit polls and in the day’s turnout, which was high practically everywhere. In North Carolina, where Biden got forty-three per cent of the vote and finished nineteen points ahead of Sanders, voters said by almost two to one that they would rather nominate a candidate who could defeat Trump than a candidate who agreed with them on the major issues. In liberal Massachusetts, where Biden came from nowhere to win by almost seven points, the exit-poll findings were virtually identical.

In South Carolina, more people voted than in the epic 2008 primary that featured Barack Obama and Hillary Clinton. On Tuesday, the same thing happened in Virginia, where 1.3 million people voted. In both of these states, the exit polls showed Biden getting more than sixty per cent of the African-American votes, a pattern replicated in Alabama and Tennessee. He also did very well in suburban areas. In the fast-growing counties of northern Virginia, he received about half the vote, defeating Sanders by more than twenty-five points. Did white-collar Democrats in Fairfax County, Loudoun County, and Prince William County wake up on Tuesday and decide en masse that there was a new Biden, or that they had better vote for him because Harry Reid, the former Senate Majority Leader, had just endorsed him? It seems far more likely they concluded that Biden, for all his shortcomings, had a better chance than Sanders of defeating Trump.

This pragmatic assessment could turn out to be wrong; if Biden is the nominee, it will be tested in the general election. The encouraging news for the Biden camp is that putting together a coalition of minority voters, highly educated voters, and suburban voters was something that Obama and Bill Clinton did in their electoral victories. It was also key to the Democratic Party’s success in the 2018 midterms. Less encouraging: Biden once again struggled to attract younger voters, his policy positions are somewhat uninspiring, and Tuesday’s results leave the Democrats divided. On Wednesday, the anger among Sanders voters was palpable. Another cautionary note is provided by the recent history of the Democratic Party selecting candidates who were supposed to be the safe choice: Al Gore (2000), John Kerry (2004), and Hillary Clinton (2016) all fell into this category.

Before we get to the general election, though, there is still a long way to go in the primary. Thirty-two states have yet to vote, and almost two-thirds of the pledged delegates are yet to be awarded. With Bloomberg out, Warren considering her options, and Tulsi Gabbard a marginal figure, it will be Biden versus Sanders, with Trump hovering. The President’s name won’t be on the ballots, of course. But his malign presence in the White House will continue to shape the race.