The campaign for the Democratic nomination has moved at warp speed over the past 10 days, and on Tuesday night it reached a decisive turning point. Barring something unforeseen, Democrats now know that former vice president Joe Biden will be the party’s nominee to challenge President Trump in November.

Biden scored a group of victories over Sen. Bernie Sanders (I-Vt.) on Tuesday, adding to the overwhelming — and unexpected — successes of a week ago on Super Tuesday. He romped in Mississippi, where he was expected to romp. He won handily in Missouri, where Sanders came agonizingly close four years ago. Most important, Biden won where Sanders could not afford to lose, in the general election battleground state of Michigan.

Biden remains well short of the 1,991 pledged delegates needed for a first-ballot victory at the national convention in Milwaukee in July. But with Tuesday’s results, he has solidified his lead in the delegate battle and, with the states that will hold their primaries in the next two weeks, that advantage inevitably will grow. Sanders has little time and few delegates remaining to be selected to have much chance of changing the trajectory.

Arizona, Florida, Illinois and Ohio hold primaries next Tuesday. Sanders lost all four to Hillary Clinton in 2016, in many cases by big margins. By the time those four states tally results next week, just over 60 percent of the pledged delegates will have been allocated. A week later comes the Georgia primary and probably another big Biden victory. Given the sudden momentum shift the campaigns have experienced, there is little to give Sanders any confidence that he can reverse the trends enough to overtake the surging Biden.

As a result of Tuesday’s results, Sanders and Biden now face new — and different — challenges. For Sanders, it is dealing with the question of how long to keep the fight going in a year when defeating the president is the overriding priority for Democratic voters. For Biden, it is making the pivot to a general election campaign, while bringing unity to his own party.

Sanders is no quitter. He has shown in this campaign and in 2016 that keeping on competing hard and arguing his case are his default positions. That’s the case even when the odds look long, as they did last fall after he suffered a heart attack and was being written out of the race, only to bounce back and, for a time, become the front-runner for the nomination.

Now he is the underdog, and distinctively so, thanks to the rapid, unprecedented coalescence around Biden’s candidacy by former rivals and millions of voters. That leaves Sanders — not at this moment perhaps but sooner than he might like — with the question of how long and how hard he will try to battle against the former vice president and what he will urge upon his passionate following.

Sanders has said repeatedly that the Democratic candidate who has the most delegates — even if that is a plurality and not a majority — should be selected as the party’s presidential nominee. He first said that when he believed he would be that candidate. Today, every bit of arithmetic and modeling says that candidate is Biden, with the odds growing that the former vice president could assemble a majority rather than just a plurality of the delegates going into the convention.

Asked Sunday by ABC’s George Stephanopoulos whether he would drop out of the race if it were clear that he could not win a plurality, Sanders hedged.

“Look, we will fight for every vote that we can, as we’re — as we try to win this election,” he said. “I’m not a masochist who wants to stay in the race that can’t be won. But right now, that’s a little bit premature. Let’s not determine what will happen on Tuesday, what will happen in the future.”

In that interview, Sanders put down his own markers for success. He said that he believed he had “a great chance” to win in Michigan and Washington. Michigan was the state that brought his candidacy back to life four years ago when he shocked Clinton by narrowly winning the state. On Tuesday night, the state fell into Biden’s column not long after the polls closed. It was as crippling a loss as Sanders has suffered this year.

Meanwhile, the results in Washington were just beginning to be reported Tuesday night. But even if Sanders were to win Washington, the delegate split would be far narrower than it was four years ago, when the state’s contest was a caucus rather than a primary and he won it with more than 70 percent of the vote.

Four years ago, Sanders balked at endorsing Clinton even at the close of the primaries, after she had won in California and her victory was secured. That led to difficult negotiations between the two camps and a contentious opening to the Philadelphia convention. This year, many Democrats say the party cannot afford to go through a repeat of that experience. What Sanders decides about his candidacy will have a profound effect on efforts to unify the party before, not after, the convention.

But this is more than an issue for Sanders. It is of enormous consequence for Biden as well. Unity demands something of those on the losing side, but it often requires much more of the winning side. Sanders has a following, especially among young voters, for a reason. He has identified ills in an unequal economic system that they are feeling acutely. Biden has fared poorly among younger voters in part because Sanders and his agenda speak to them in ways Biden and his message do not.

Biden and his team have other work to do and less time than it might seem to get it done. Even if Sanders chooses to keep running far into the spring, Biden will have to begin to make a swift pivot toward the general election, with the goal of turning a campaign operation that has drawn criticism even from prominent supporters into a machine capable of waging a general election against the Trump forces.

Biden won states on Super Tuesday where he had spent little or no money, in states where he had held no rallies. He was winning because nearly two-thirds of Democrats appeared to be looking for a more moderate alternative to Sanders and Biden was the last candidate standing. The deficiencies in his organization that contributed to his loss in Iowa cannot go unattended, say sympathetic Democrats.

Biden will start a general election campaign many months behind the Trump campaign in identifying the voters who will make the difference in November and communicating directly to them. For the November election, he will need to scale up his operation, sharpen his message and reach beyond to voters who either shifted to Trump in 2016 or sat on the sidelines.

Trump remains the great unifier of Democrats, but it will take something more on the part of both Sanders and Biden to bring the party fully and enthusiastically together if the party is to be ready for what promises to be a general election that voters in both parties see as the most important in their lifetimes.