DEARBORN HEIGHTS, Mich. — Former vice president Joe Biden seized control of the Democratic presidential contest Tuesday with four victories, including a decisive win in Michigan that struck a devastating blow to Bernie Sanders's ambitions after the senator from Vermont committed his campaign to winning the key Midwestern swing state.

Biden also scored resounding wins Tuesday in Mississippi, Missouri and Idaho while two other states — North Dakota and Washington — continued to count ballots.

“It’s more than a comeback. . . . It’s a comeback for the soul of this nation,” Biden said at the National Constitution Center in Philadelphia as he made explicit efforts to reach out to all parts of the party. “This campaign is taking off, and I believe that we are going to do well from this point on.”

The results showed further evidence of the powerful coalition that Biden has assembled to fuel his remarkable turnaround in the past few weeks, particularly black voters who form the backbone of the Democratic Party and the suburban women who helped drive record turnout for Democrats in the 2018 elections. Biden has also been winning white Democratic voters without a college degree, an important constituency that Donald Trump successfully courted in 2016. The former vice president even outperformed Sanders in some of the state’s college communities.

Former vice president Joe Biden continued his Super Tuesday momentum in the six states participating in the March 10 primaries and caucuses. (The Washington Post)

Democratic voters have demonstrated over the past week, in exit polls and at the ballot box, that they want to avoid the protracted primary battle of 2016 and quickly coalesce behind a nominee who can begin focusing on trying to defeat President Trump.

A drumbeat has come from party operatives and officials that Biden is the putative nominee and that the fight for the nomination is concluding.

It was unclear on Tuesday night how fierce that fight would be going forward, with Sanders deciding not to make any public remarks following his disappointing finish.

National politics reporter Matt Viser explained how former vice president Joe Biden's Super Tuesday win reshaped the Democratic presidential race. (The Washington Post)

In his address, Biden said his campaign was “regenerating the Democratic Party,” and he reached out to Sanders supporters, thanking them “for their tireless energy and their passion.”

“We share a common goal, and together we’ll defeat Donald Trump,” he said.

On a night when he was the only candidate speaking, Biden also made appeals to Republicans and independents.

“Tonight we are a step closer to restoring decency, dignity and honor to the White House,” he said. “At this moment, there’s so much fear in the country. There’s so much fear across the world. We need presidential leadership that’s honest, trustworthy, truthful and steady.”

The wins for Biden come at a time when the presidential race is facing major disruption from the repercussions of the spread of the novel coronavirus. As voters streamed to the polls Tuesday, election workers used hand sanitizer and regularly disinfected voting equipment and in some places supplied medical-grade disposable gloves for voters to use with touch-screen consoles.

The outbreak also affected candidate schedules, with Biden and Sanders canceling their planned rallies in Cleveland on Tuesday night, forgoing a major election night spectacle that campaigns use to communicate with voters and make small-dollar fundraising appeals. While Biden traveled to Philadelphia, where he gave his post-election remarks to staffers who came from the campaign’s nearby headquarters, Sanders went home to Burlington, Vt.

The rally cancellations came after Ohio Gov. Mike DeWine declared a state of emergency and requested that indoor athletic events in the state take place without spectators. Ohio is due to vote on March 17.

“We will continue to consult with public health officials and public health guidance and make announcements about future events in the coming days,” Biden deputy campaign manager Kate Bedingfield said in a statement.

The Biden campaign announced shortly afterward that it was canceling a Thursday event in Tampa. Instead, the campaign said, Biden will give an address on the coronavirus response from his hometown of Wilmington, Del.

In 2016, Sanders beat former Secretary of State Hillary Clinton in all but two of the states voting Tuesday — Mississippi and Missouri. But Idaho and Washington held caucuses that year, with lower turnouts that benefited Sanders. Those contests were converted to statewide primaries for this year, in part at the urging of Sanders supporters who wanted to increase participation. North Dakota changed its caucus procedures to allow Democrats to participate throughout the day.

The key test for both candidates Tuesday was Michigan because it provides an important barometer for how they would do in one of the typically Democratic, industrial Midwestern states that Trump won. The state’s voting coalition, with large blocs of students, working-class whites, union-affiliated African Americans and a major Muslim population, was cited by Sanders advisers as a potential showcase for the coalition he hoped to build.

Over the weekend, Sanders canceled events outside of Michigan and rushed his campaign team into the state, staging an all-out blitz for voters while Biden campaigned across a span of Tuesday-voting states. But earlier on Tuesday, Sanders stopped short of predicting a repeat victory in the state.

“Let’s not say what you have to win,” Sanders told reporters outside a voting location in Dearborn Heights, Mich. “We’ve got a whole lot of delegates to go.”

Amid Sanders’s silence as the votes came in, a key ally acknowledged the disappointment.

“There’s no sugarcoating it; it’s a tough night tonight. It’s a tough night for the movement overall,” said Rep. Alexandria Ocasio-Cortez, who endorsed Sanders in the fall. She later said that while it was “a tough night electorally,” Sanders had done well among younger voters.

Preliminary exit polls of Michigan voters casting ballots Tuesday did show that Sanders supporters were far more likely to say they are enthusiastic about his candidacy than Biden backers. Over 8 in 10 voters who supported Sanders said they would be enthusiastic if he wins the nomination, compared with less than 6 in 10 voters who supported Biden who held a similar view about their candidate.

The share of black voters was on track to be about the same as last cycle, making up 1 in 5 voters. In 2016, Sanders won among white voters, while Hillary Clinton won 68 percent of black voters.

In one sign that most of the party is prepared to unify behind whichever candidate emerges, about 9 in 10 of Biden’s supporters said they would support the party’s nominee, according to early exit polls in Michigan, Missouri and Washington. Across those three states, at least 8 in 10 Sanders voters said they would vote for the Democratic nominee in the general election.

Black voters in Mississippi made up almost two-thirds of the electorate, with more than 8 in 10 going for Biden, similar to the 9 out of 10 that Clinton won in 2016. Fueling Biden further was two-thirds support among white voters, a group more typically aligned with Sanders.

In Missouri, Biden won 3 out of 4 black voters, and voters who made up their mind in the past few days or earlier in March voted almost 2 to 1 in favor of Biden. Roughly two-thirds of Missouri Democratic primary voters said they attend religious services at least occasionally, according to preliminary exit polls. Biden won roughly 7 in 10 of those voters.

There are few game-changing opportunities left for Sanders. The candidates are scheduled to face off in a two-hour debate on Sunday night in Phoenix, perhaps the last chance for a shift. Next Tuesday, four more states will vote: delegate-rich Florida, Illinois, Ohio and Arizona.

A spokeswoman for the Democratic National Committee said Tuesday there were no plans to cancel the Arizona debate, though organizers continue to speak daily with local health officials. The DNC did alter the format, however, by banning the live audience that has attended each of the previous debates. Attendees are being cautioned by the party to follow Centers for Disease Control and Prevention guidelines, which include avoiding public gatherings while suffering potential symptoms of the coronavirus.

The only candidate remaining aside from Sanders and Biden is Rep. Tulsi Gabbard (D-Hawaii). She has collected delegates in only one contest, the caucuses held last week in American Samoa, and did not qualify for the debate. Entering the contests Tuesday, Biden enjoyed a lead in the delegate race.

Biden has been boosted in recent weeks by the Democratic Party closing ranks behind his candidacy. He has received endorsements of many of his major opponents in the primary fight, including Sen. Amy Klobuchar (D-Minn.), Rep. Beto O’Rourke (D-Tex.), Sen. Cory Booker (D-N.J.), Sen. Kamala D. Harris (D-Calif.), former New York mayor Mike Bloomberg and former South Bend, Ind., mayor Pete Buttigieg.

Another former rival, businessman Andrew Yang, who supported Sanders in 2016, endorsed Biden on Tuesday after the early results.

“The math shows Joe is our prohibitive nominee,” Yang said on CNN. “We need to bring the party together. We need to start working on defeating Donald Trump in the fall.”

Sen. Elizabeth Warren (D-Mass.), who dropped out last week, has not endorsed either Biden or Sanders.

Supporters of Sanders have complained about Warren’s decision not to endorse Sanders, whom many of her supporters saw as a second choice.

“Imagine if the progressives consolidated last night like the moderates consolidated, who would have won?” Rep. Ilhan Omar (D-Minn.) tweeted after the March 3 primaries. “That’s what we should be analyzing.”

In a sign of further consolidation, Priorities USA, the largest Democratic super PAC focused on the presidential race, announced Tuesday that it would prepare advertising to defend Biden against Republican attacks over the coming months, as his campaign continues to compete in the primaries. The group said the support was a result of his standing in the race and not an endorsement of his campaign.

“I think there is a recognition that we cannot win the election in the next few months, but we can lose it,” Priorities Chairman Guy Cecil said in an interview Tuesday. “We are not going to hold back just because the primary is ongoing.”

American Bridge, another group working to defeat Trump, also promised on Tuesday night to shift its efforts to support Biden. “Tonight the voices of Democratic voters are loud and clear: They want Joe Biden to be our standard-bearer,” said Bradley Beychok, the president of American Bridge.

Rep. James E. Clyburn (D-S.C.), a top Biden ally, called on the Democratic National Committee to halt further primaries and any additional debates if Sanders failed to carry any states on Tuesday.

“If the night ends the way it has begun, I think it is time for us to shut this primary down, it is time for us to cancel the rest of these debates,” he told NPR. “because you don’t do anything but get yourself in trouble if you continue in this contest when it’s obvious that the numbers will not shake out for you.”

The sniping between the campaigns has grown more intense over the past several days, although the candidates themselves have largely refrained from the kind of vitriolic debate that has marked previous campaigns.

There remains significant Democratic concern about Biden’s ability to rapidly scale up his campaign in the coming months to face Trump.

On Tuesday morning, Biden let out an expletive when challenged by a member of the International Brotherhood of Electrical Workers union over his gun control plans.

The man told Biden that he was trying to “end our Second Amendment rights.”

After cursing, Biden added: “I’m not taking your gun away. I did not say that.”

As Biden and the man went back and forth, union members and campaign staffers tried to intervene, saying there were other people trying to greet the former vice president.

When Sanders campaign manager Faiz Shakir shared a Republican video of the encounter, other Democrats pounced, suggesting that the Sanders campaign was simply parroting GOP talking points.

Shakir later deleted the tweet.

Patrick Moynihan and Dan Keating contributed to this report.