“Sanders should start thinking through what outlet he has to draw concessions from Biden, and it’s not clear to me that continuing a presidential campaign that does not have a path to victory is one of those options,” says Sean McElwee, a co-founder and the executive director of the liberal research and advocacy group Data for Progress, which has been polling extensively in the primary states. “I think he should … think soberly about the reality. I don’t think there are any states right now he is favored to win.”

Read: Bernie Sanders has a choice to make

Others on the left did not go so far. The Progressive Change Campaign Committee, which had endorsed Senator Elizabeth Warren of Massachusetts before she withdrew, issued a statement last night urging Sanders to remain in the race at least through the debate, which will be held Sunday in Phoenix. Robert Reich, a leading liberal economic and policy analyst and a former labor secretary under Bill Clinton, said the same.

“People are going to be asking themselves as they watch that debate who is going to be better able to take on Trump one-on-one,” Reich said. “The stampede toward Biden was remarkably fast. That shows that his support is not absolutely steadfast, so it’s at least possible that if his debate performance is very bad on Sunday, Bernie Sanders could have a renaissance.”

But across much of the party, Biden’s triumphs in Michigan, Missouri, Mississippi, and Idaho confirmed the message sent by his victories on Super Tuesday: that the question is no longer whether, but when, the former vice president becomes the party’s nominee against Donald Trump.

As in last week’s contests, Biden last night dominated among African Americans; led among college-educated white voters; and even topped Sanders, albeit more narrowly, among blue-collar white voters, who had preferred the senator in each of the year’s first four contests. Compounding Sanders’s problem across the country, the young voters who generally preferred him by large margins over Biden consistently represented a smaller share of the total vote than they did four years ago, according to exit polls conducted by Edison Research for a consortium of media organizations.

“If he’s not going to win working-class [white voters], and he’s going to lose [black voters] massively, and the turnout is all with his opponent’s people and not his … there is just no path to victory,” says Tad Devine, who served as a senior strategist for Sanders in 2016 but is unaffiliated with any campaign this year. “It’s just that simple.”

Biden tried to project confidence in his victory speech last night, delivering conspicuously calm and measured remarks focused on the general election. And he offered the kind of conciliatory praise for Sanders that usually comes at the end of a primary race. “We share a common goal, and together we will defeat Donald Trump,” Biden said. “We will defeat him together.” Sanders, meanwhile, spoke volumes about his precarious situation by choosing not to speak until today.