Democrats gathered in Chicago for the opening night of their convention more united and energized than at any time since they nominated Barack Obama 16 years ago. Gone was the feeling that they were fighting just to keep Donald Trump out of the White House. Instead, there was a feeling that they were fighting for something.

And yet there was also a certain nostalgia among the thousands of delegates. Many of them were elected on the promise of supporting Joe Biden, and until last month they believed they had come here for exactly that reason.

When Kamala Harris made a surprise appearance on stage after 9 p.m., the United Center erupted in cheers at the party’s new savior, but she quickly recognized the man she had replaced on the ballot.

“I want to kick things off with a celebration of our incredible President Joe Biden,” Harris said. “Joe, thank you for your historic leadership, for your lifelong commitment to our nation and for all that you continue to do; we are eternally grateful,” as the crowd, not for the first time that night, chanted in response, “Thank you, Joe!”

“I was disappointed and shocked” when Biden withdrew, said Dan Farfaglia, a delegate from upstate New York who wore a “Biden 46” jersey and a “Yes, we did” hat. “He already had all the delegates he needed to win the nomination.”

For all the coconut-flavored good vibes, there was an unmistakable feeling among some in the audience that the mood would have been just as good if this had been Biden’s convention, and that Harris’ positive poll rating could have been attributed to him.

It remains an article of faith among Harris’ campaign staff, most of whom were Biden’s campaign staff until a month ago, that if Biden had stayed in the race, he would have ultimately won. (Not to mention his disastrous debate performance, his shaky follow-up, and the party’s furor over his candidacy.) Biden, they like to point out, is the only politician to have defeated Trump, and by November, core Democratic voters who were unenthusiastic about the prospect of a president staying in office until he was 86 would finally have come home, if only to avert the threat of a second Trump term.

“I am absolutely convinced he would have won,” said JB Pritzker, governor of Illinois and de facto host of the convention. “I fought hard to give him the opportunity, but I also respect the fact that he chose not to do it.”

“Of course,” said Rep. Tom Suozzi of New York when asked if Biden could have won. “There’s no doubt that with his record and Trump’s record, he had a good chance of winning.”

“Do you know Allen Lichtman?” asked Tom Daschle, the former Senate majority leader, referring to an American University history professor who rose to social media fame earlier this year when he posted a theory he developed in 1996 about what it would take to win the presidency. “He has correctly predicted every election, right? And the day before President Biden announced he would not run, he suggested that Biden was very likely to win. I think it’s a question of certainty. Allen Lichtman says we probably won, but I think we’re taking some of the uncertainty off the table.”

When Biden delivered his speech long after his scheduled time and Americans on the East Coast had at least already gone to bed, it created one of the most electrifying moments of the evening when delegates chanted “We love Joe” for more than four minutes.

“Our best days are not behind us, they are ahead of us,” Biden said in a forceful speech in which he listed his political and strategic successes of the past four years. “Democracy has won. Democracy has delivered. And now democracy must be preserved!”

“This Joe Biden,” said a Democratic strategist after the speech, “beats Donald Trump by 15.”

Not everyone buys it.

“He had no chance,” said Dean Phillips, the Minnesota congressman who launched a hopeless campaign against Biden that was intended to be little more than a surrogate campaign for voters to express their dissatisfaction with Biden’s age. “It’s not about what I thought about his age, it’s about what the American voters thought about his age, and they said what they thought loud and clear.”