Democratic presidential candidate former Vice President Joe Biden, accompanied by his wife Jill arrives to speak to members of the press at the National Constitution Center in Philadelphia, Tuesday, March 10, 2020. (AP Photo/Matt Rourke)

Democratic presidential candidate former Vice President Joe Biden, accompanied by his wife Jill arrives to speak to members of the press at the National Constitution Center in Philadelphia, Tuesday, March 10, 2020. (AP Photo/Matt Rourke)

WASHINGTON (AP) — Joe Biden decisively won Michigan’s Democratic presidential primary, seizing a key battleground state that helped propel Bernie Sanders’ insurgent candidacy four years ago. The former vice president’s victory there, as well as in Missouri, Mississippi and Idaho, dealt a serious blow to Sanders and substantially widened Biden’s path to the nomination.

Biden again showed strength Tuesday with working-class voters and African Americans, who are vital to winning the Democratic nomination.

Sanders won North Dakota and awaited results from Washington state, where all votes are cast by mail or by dropping them off in a ballot box. Washington’s primary was too early to call Wednesday evening. Following the release of updated results, Biden led Sanders by a little more than 16,000 votes out of nearly 1.2 million counted, or a margin of 1.4 percentage points.

The six-state contest Tuesday marked the first time voters weighed in on the primary since it effectively narrowed to a two-person race between Sanders and Biden. And the first four states on Tuesday went to Biden, a dramatic reversal for a campaign that appeared on the brink of collapse just two weeks ago.

Now it is Sanders, whose candidacy was ascendant so recently, who must contemplate a path forward. He said at a news conference in Vermont on Wednesday afternoon that he will stay in the race and plans to appear at the Democratic debate against Biden on Sunday.

Addressing supporters in Philadelphia, Biden noted that many had “declared that this candidacy was dead” only days ago, but “now we’re very much alive.” He also asked Sanders supporters to back him going forward.

“We need you, we want you, and there’s a place in our campaign for each of you. I want to thank Bernie Sanders and his supporters for their tireless energy and their passion,” Biden said. “We share a common goal, and together we’ll beat Donald Trump.”

Full Coverage: Election 2020

Even as the contours of the race came into shape, however, new uncertainty was sparked by fears of the spreading coronavirus . Both candidates abruptly canceled rallies in Ohio that were scheduled for Tuesday night.

Sanders’ campaign also said all future events would be decided on a case-by-case basis given public health concerns, while Biden called off a scheduled upcoming Florida stop. He also announced that Friday and Monday stops in Florida and Illinois would be turned into virtual events. Still, the former vice president said Tuesday night that he’d be announcing plans to combat the coronavirus later this week.

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The Democratic National Committee also said that Sunday’s debate between Sanders and Biden would be conducted without an audience .

Among former White House hopefuls and leaders of powerful liberal groups, however, Biden’s momentum is now undeniable.

Bradley Beychok, president and co-founder of American Bridge 21st Century, a liberal super PAC, said his group “will be ALL IN to elect @JoeBiden as our next president.” The organization is spending millions of dollars trying to win over people who backed President Donald Trump in key states in 2016.

Guy Cecil, chairman of the flagship Democratic outside political organization Priorities USA, tweeted: “The math is now clear. 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.”

There were other major warning signs for Sanders on Tuesday. He again struggled to win support from black voters. About 70% of Mississippi’s Democratic primary voters were African American, and 86% of them supported Biden, according to an AP VoteCast survey of the electorate.

After Sanders upset Hillary Clinton in Michigan four years ago, his loss there Tuesday was particularly sobering. It undermined his argument that he could appeal to working-class voters and that he could expand the electorate with new young voters.

One of the few bright notes for Sanders was his strength among young voters, but even that has a downside because they didn’t turn out enough to keep him competitive. Sanders won 72% of those under 30 in Missouri and 65% in Michigan, according to AP VoteCast. The senator was also about even with Biden among voters ages 30 to 44.

Sanders’ mathematical path to winning enough delegates for the nomination is rapidly disappearing.

Sanders now needs 57% of the delegates not won so far to get to 1991, the magic number to win the nomination. Both delegate allocation math and voting history show how unlikely it is for Sanders to hit that goal and overtake Biden.

“There’s no sugarcoating it. Tonight’s a tough night,” New York Rep. Alexandria Ocasio-Cortez, one of Sanders’ highest-profile supporters, said on Instagram. “Tonight’s a tough night for the movement overall. Tonight’s a tough night electorally.”

Another top Sanders backer, Minnesota Rep. Ilhan Omar, tweeted: “Yes we are a family, united in restoring our democracy and committed to defeating Trump, but that doesn’t mean we should stop fighting for the candidate that best represents our policy priorities in this Primary.”

According to an Associated Press analysis , Biden picked up at least 184 new delegates in Tuesday’s voting while Sanders got 112. Biden now has 864 overall, while Sanders has 710.

Although six states voted, Michigan, with its 125 delegates, got most of the attention. Trump won the state by only 10,704 votes during the general election, his closest margin of victory among Michigan, Pennsylvania and Wisconsin. Those states gave Trump the narrow edge in the 2016 Electoral College after Clinton won the popular vote.

In addition to the powerful groups now siding with Biden, the former vice president has picked up the endorsements of many of his former presidential rivals, including Sen. Kamala Harris, Sen. Cory Booker and entrepreneur Andrew Yang. Michigan Gov. Gretchen Whitmer, sometimes mentioned as a possible vice presidential choice, also endorsed Biden and campaigned with him.

But not every Democrat was lining up behind Biden. Michigan Rep. Debbie Dingell, who represents a sprawling district from the college town of Ann Arbor to the Detroit suburbs, said Tuesday that she’s staying neutral.

“I remember what it was like four years ago and the vitriol and the anger, the people mad at each other the whole election cycle. We can’t afford that,” Dingell said. “It’s about getting out and voting in November.”

Neither Biden nor Sanders has public events scheduled for Wednesday. And although Biden is celebrating a growing delegate lead, he’s still confronting voters who question his positions, which include a gun control plan that reinstates an assault weapons ban and includes a voluntary buyback program for assault weapons.

That issue was at the center of a testy exchange with a worker while Biden was rallying earlier Tuesday in Detroit. The man accused him of “actively trying to end our Second Amendment right.” Biden shot back, “You’re full of shit,” but went on to say that while he supports the Second Amendment, “Do you need 100 rounds?”

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Associated Press writers Mike Householder in Detroit and Seth Borenstein in Washington contributed to this report.

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Catch up on the 2020 election campaign with AP experts on our weekly politics podcast, “Ground Game.”