Joe Biden decisively won Michigan's Democratic primary on Tuesday, 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 and Mississippi, dealt a serious blow to Sanders and substantially widened Biden's path to the nomination. The Vermont senator's hopes rested on Idaho, North Dakota and Washington state, where votes were still being cast or tabulated but where far fewer delegates were at stake. Biden again showed strength with working-class voters and African Americans, who are vital to winning the Democratic nomination.

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 three large states easily 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.

Sanders did not plan to address the public on Tuesday night. Biden planned to take the stage in Philadelph Even as the contours of the race came into shape, the campaign faced new uncertainty amid fears of the spreading coronavirus. Both candidates abruptly canceled rallies in Ohio that were scheduled for Tuesday night. Sanders' campaign said all future events would be decided on a case-by-case basis, while Biden called off a scheduled upcoming stop in Florida.

The Democratic National Committee also said that Sunday's debate between Sanders and Biden would be conducted without an audience. It is unclear when they will resume large public events given that top health officials are warning that the virus in the short term will be more widespread. 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. Two-thirds of Mississippi's Democratic primary voters were African American, and three-quarters of them supported Biden.

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. His showing makes it difficult for Sanders to argue that he could win the state in November, when Democrats are desperate to rebuild their blue wall, which includes Wisconsin, Pennsylvania and Michigan.

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 70% of those under 30 in Missouri and 64% in Michigan, according to AP VoteCast. The senator was also about even with Biden among voters ages 30 to 44.

Although six states voted on Tuesday, 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.

Sanders flew home to Vermont on Tuesday and didn't immediately make any public statement. He's vowed not to drop out regardless of the results and frequently rails against the “Democratic establishment” that he says has aligned against him. 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, as of Tuesday, entrepreneur Andrew Yang.

Michigan Gov. Gretchen Whitmer, sometimes mentioned as a possible vice presidential choice, also endorsed Biden and campaigned with him ahead of Tuesday's primary. Not every Democrat was lining up behind Biden, though. 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.” Like Sanders, Biden has no public events scheduled for Wednesday. And though he's 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 Tuesday in Detroit.