Joe Biden won the crucial Michigan primary on Tuesday, as well as Mississippi, Idaho and Missouri, with results in North Dakota and Washington yet to be called.

The victories for the former vice president were a huge blow for Bernie Sanders in the race to be the Democratic nominee to take on Donald Trump in November's presidential election.

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Five takeaways from Tuesday's primaries

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Spotlight: Bernie Sanders, a progressive prophet

In a measured speech after the scale of victory became clear, Biden praised Sanders and his supporters, stressing the importance of unity and honest leadership. Perhaps tellingly, Sanders chose not to speak on Tuesday evening, instead returning to his home state of Vermont. 

Biden currently leads Sanders in the delegate race by 823 to 663, according to the AP Delegate Tracker, with 1,991 needed for a majority. The former vice president holds strong polling leads in the high-delegate contests in Florida and Arizona next week. 

'A progressive vision'

Biden immediately reached out to Sanders supporters in the wake of Tuesday's victories, promising a "bold, progressive vision" and praising the Vermont senator's backers.

"I want to thank Bernie Sanders and his supporters for their tireless energy and their passion," the 77-year-old said. "We share a common goal, and together we'll defeat Donald Trump."

Biden also namechecked the long list of former rivals who have endorsed him, and drew contrasts with Trump, saying that in a time of fear in America leadership that is "honest, trusted, truthful and steady... reassuring" is needed. 

"Tonight we are a step closer to installing decency, dignity and honor to the White House," he added, before hitting touchstone issues such as gun rights, healthcare and education. 

Tough night for Sanders

Sanders' decision to give up free airtime on Tuesday night and instead consider the way forward is unusual. He had staked a lot on Michigan, and looked set to lose by double digits with votes still being counted.

He was neck-and-neck with Biden in Washington and ahead in North Dakota with votes still being counted. 

Key Sanders surrogate Alexandria Ocasio-Cortez said on Instagram: "There's no sugar-coating it – tonight's a tough night. Tonight's a tough night for the movement overall."

The Vermont senator now has choices to make both as to whether to stay in the race and how to approach it if he does. 

Decisive Biden wins

Biden won in Mississippi by 65 points, with Sanders was struggling to hit the 15 percent threshold needed to win statewide delegates. The former vice president took Missouri by 25 points and Idaho by around seven points. 

Sanders beat Hillary Clinton in 125-delegate Michigan, a key battleground state that Donald Trump flipped from the Democrats in the 2016 presidential election, but Biden was on course to win by around 15 points on Tuesday.

Exit polls suggested Biden was continuing his success with African American voters as well as Democrats concerned with electability, and also had strong support from female and working class voters. 

Biden won 84 percent of black voters in the Mississippi primary to 13 percent for Sanders, according to exit polls, and 80 percent of voters who prioritized someone who could beat Trump.

Coronavirus impact

Both campaigns are now also dealing directly with a new dynamic: the coronavirus. The number of coronavirus cases in the U.S. surpassed 1,000 on Tuesday. 

Biden and Sanders called off rallies in Ohio, which votes next week, on Tuesday evening, and the former vice president canceled a rally scheduled to take place in Florida.

The Democratic National Committee also said there would be no audience in the room for Sunday's debate between Biden and Sanders.