Former US vice president Joe Biden scored commanding victories in Michigan and two other states, taking a big step toward the Democratic Party's presidential nomination and dealing a blow to rival Bernie Sanders' fading White House bid.
Mr Biden won over voters of all types to easily capture Missouri and Mississippi on a day when six states made their choices in the race to pick a challenger to Republican President Donald Trump.
The sweeping wins put Mr Biden, 77, on a path to the nomination to face Mr Trump in the 3 November election, while narrowing the path for Sanders, 78, who had hoped for an upset win in Michigan to keep his White House hopes alive.
Mr Sanders' loss in a state he won in the 2016 Democratic primary will increase pressure on the democratic socialist US senator from Vermont to exit the race and help Democrats prepare for a bruising election campaign against Mr Trump.
Voters across the states that voted said they trusted Mr Biden more to handle a major crisis by roughly 2-to-1over Mr Sanders, exit polls by Edison Research showed, a possible sign the fast-spreading coronavirus outbreak helped increase Mr Biden's appeal as a steady and experienced hand.
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Speaking in Philadelphia, Mr Biden thanked Mr Sanders and his supporters for their energy and passion and appealed for party unity.
"We share a common goal and together we are going to defeat Donald Trump," said Mr Biden, who also mentioned his former rivals such as Pete Buttigieg, Amy Klobuchar and Kamala Harris who endorsed him after dropping their own presidential bids.
"Winning means uniting America. Not sowing more division and anger," Mr Biden said.
Mr Sanders, who returned home to Vermont last night, did not plan a public statement, a departure from his usual practice on primary nights.
With 83% of precincts reporting, Mr Biden led in Michigan with 53% of the vote to 38% for Mr Sanders. Edison Research projected the primary turnout of 1.7 million would surpass the 1.2 million who voted in 2016.
In Washington state, Mr Biden and Mr Sanders were in a virtual tie with more than two-thirds of the votes counted.
Michigan was the biggest and most competitive of the six states that held nominating contests yesterday, which also included North Dakota and Idaho. It also is a crucial battleground that Trump narrowly and unexpectedly won in 2016, which along with wins in Pennsylvania and Wisconsin propelled his ascent to the White House.
The Biden breakthrough in Michigan, along with his dominant victories in Missouri and Mississippi, could be too much for Mr Sanders to overcome, with the contest shifting to large states including Florida, Ohio and Georgia where Mr Biden is seen as a clear favourite.
By the end of March, about two-thirds of the nearly 4,000 delegates to July's Democratic nominating convention will be allocated.
So far yesterday, Mr Biden had won 103 delegates to Mr Sanders'48, giving him an overall lead of 731-593 in the race for the1,991 delegates needed for the nomination, according to Edison Research.
"The math says Joe is our prohibitive nominee. We need to bring the party together," former presidential candidate Andrew Yang said on CNN as he endorsed Mr Biden.
One of Mr Sanders' most influential supporters, liberal US Representative Alexandria Ocasio-Cortez, acknowledged the depth of his defeat.
"There's no sugar coating it," she said on Instagram. "Tonight's a tough night."
Both candidates called off planned rallies in Cleveland today because of concerns over the coronavirus outbreak, which has rattled markets and prompted Democrats to criticise the Trump administration's response.
Mr Biden was powered to victory yesterday by strong support from a broad coalition of groups, including women, African Americans, those aged 45 and older, union members and all but the very liberal, according to exit polls.
In Michigan, he performed well with union members and working-class white voters - two groups that helped Mr Sanders to an upset victory over Hillary Clinton in the state in 2016 but did not turn out as strongly for him this time despite Mr Sanders' economic populism and his call for universal healthcare.
Mr Sanders won large majorities of voters under 30-years-old in Michigan, Missouri and Mississippi, yet that group had a smaller impact on the results this year. Voters between 18 and 29 made up 12% of the Democratic primary electorate in Missouri, 10% in Mississippi and 15% in Michigan, down at least 4 percentage points in each state from 2016.
Two of the largest Democratic Super PACS said they were going to begin working for Mr Biden. American Bridge President Bradley Beychok announced the group planned a $2.2 million ad buy in Pennsylvania for Mr Biden.
"The math is now clear. Joe Biden is going to be the Democratic nominee," Priorities USA Chairman Guy Cecil said on Twitter, adding the group would "do everything we can to help him defeat Donald Trump."
