Joseph R. Biden is on a primary roll across the South and Midwest.
The former vice president scored wins Tuesday in Michigan, Mississippi, Missouri and Idaho to beef up his lead over Sen. Bernard Sanders, putting a serious and potentially fatal dent in the Vermont socialist’s dreams of becoming president.
Mr. Biden was projected to be the winner in Michigan, the biggest prize of the six states that voted Tuesday. He led 53% to 41% with about 50% of the precincts reporting.
As he closed in on the nomination, Mr. Biden struck a humble tone and spoke of unifying the Democratic Party to beat President Trump.
“Tonight we are a step closer to restoring decency, dignity and honor in the White House. That’s our only goal,” he said.
Reaching out to Mr. Sanders’ supporters, Mr. Biden said pledged to “deliver a bold, progressive vision to the American people.”
Mr. Sanders and his campaign for a far-left political revolution had the most riding on the balloting across a half-dozen states where 352 delegates were to be awarded.
The 78-year-old avowed socialist’s lead slipped away to Mr. Biden in the Super Tuesday contests last week. He was focused on avoiding a stinging defeat in Michigan, where voters resuscitated his presidential bid four years ago by giving him a surprise win over former Secretary of State Hillary Clinton.
Mr. Biden, meanwhile, was looking to build on the momentum he carried out of a win Feb. 29 in South Carolina and 10 victories across the Super Tuesday states.
Priorities USA Action Chairman Guy Cecil, who leads the largest Democratic super PAC, said it is time for the party to rally behind Mr. Biden.
“The math is now clear,” he tweeted. “Joe Biden is going to be the Democratic nominee for president and @prioritiesUSA is going to do everything we can to help him defeat Donald Trump in November.”
House Majority Whip James Clyburn of South Carolina, the nation’s top elected Democrat, said Mr. Sanders has to win at least one of the six states, or else the party establishment should “shut this primary down [and] cancel the rest of these debates.”
Mr. Biden’s success has been fueled by black, older and white working-class voters.
Mr. Sanders has been the preferred candidate of younger voters and Hispanics, but youths have not turned out in large enough numbers in most states to push Mr. Sanders across the finish line.
Those trends continued Tuesday as Mr. Biden won 84% of black voters in Mississippi and 69% of them in Missouri. He also was the top pick of older voters and those who said they most want a candidate who can defeat Mr. Trump.
The races in Mississippi and Missouri were called as soon as the polls closed at 8 p.m. Four years ago, Mr. Sanders came within a whisker of winning the Missouri primary.
Mr. Biden won Idaho and Mr. Sanders nabbed North Dakota, but the results of Washington state were too close to call as of early Wednesday morning.
In Republican primaries, Mr. Trump swept the contests and chalked up a decisive win in Michigan, which will be a crucial general election battleground.
In 2016, Mr. Trump flipped it into the Republican column for the first time in two decades to punch his White House ticket. But he won by the narrowest of margins, and Democrats are pulling out all the stops to take back Michigan in November.
In Michigan, Missouri and Washington, Mr. Trump loomed large in the minds of Democratic primary voters as they weighed their candidates.
Exit polls showed that a majority of voters in these states were more interested in nominating a candidate they think can win against Mr. Trump than someone who agrees with them on issues.
Yet only 45% of Democratic primary voters in Missouri said they would be “enthusiastic” with Mr. Biden at the top of the party’s ticket, according to exit polls.
That response signaled that Mr. Biden has some work to do if he is to energize his party for a general election matchup against Mr. Trump.
Another 31% said they would be satisfied but not enthusiastic with Mr. Biden, according to CNN’s tally of the exit polling data.
Mr. Sanders fared worse, with 31% enthusiastic and another 30% satisfied should he emerge the standard-bearer.
A majority of voters in Michigan and Missouri also said they trust Mr. Biden more than Mr. Sanders to handle a major crisis. A plurality of voters in Washington agreed.
Both the Sanders and Biden campaigns had scheduled large rallies in Ohio for Tuesday evening’s results but canceled them over coronavirus concerns at large public gatherings.
Sanders campaign manager Faiz Shakir posted a video of Mr. Biden’s altercation with the gun owner.
Mr. Biden entered Tuesday with a 670 to 574 lead over Mr. Sanders in the race for the 1,991 delegates needed to win the nomination outright. He was poised Tuesday night to extend that lead to a couple of hundred delegates.
Rep. Tulsi Gabbard of Hawaii, who has continued her quixotic campaign with no chance of winning, was on the board with a pair of delegates she won in American Samoa.
The contests on Tuesday played out amid the novel coronavirus outbreak that sent stock markets plummeting and fanned public fears.
They also were held days after Sen. Elizabeth Warren of Massachusetts pulled the plug on her campaign. Pressure intensified on her in recent days to pick sides in the Democratic race.
New York Mayor Bill de Blasio, whose far-left presidential campaign fell flat in the span of four months, urged fellow liberal Ms. Warren to endorse Mr. Sanders.
“Now our progressive movement needs her more than ever,” Mr. de Blasio said on Twitter. “Senator, if the shoe was on the other foot @BernieSanders would have endorsed you already. Please join us!”
The largest shares of delegates up for grabs Tuesday were in Michigan, with 125, and Washington, with 89. The candidates also were battling for 68 delegates in Missouri, 36 in Mississippi, 20 in Idaho and 14 in North Dakota.
Mr. Sanders carried Idaho, Washington and North Dakota in 2016.
The next major stops in the nomination battles are next week when voters in Arizona, Florida, Illinois and Ohio head to the polls. Voters in the Northern Marianas, Georgia, and Puerto Rico also will cast ballots this month.
The two candidates are also scheduled to face off on the debate stage Sunday in Phoenix, though event organizers announced Tuesday that there would be no live audience out of an abundance of caution over the coronavirus.
⦁ David Sherfinski and Stephen Dinan contributed to this report.