Democratic presidential candidate Bernie Sanders will “assess his campaign” after suffering more losses to Joe Biden in Tuesday’s primary contests.
Mr Biden won in all three states to hold votes, expanding his lead.
Mr Sanders will discuss his options with supporters, his campaign said.
Meanwhile, Mr Biden appealed to Sanders backers to anoint him as the Democrat nominee to face President Donald Trump in November.
What are the results so far?
Mr Biden, 77, won a big victory over Mr Sanders, 78, in Florida, the biggest prize of the night with 219 delegates.
The former vice-president won 62% of the vote and about 130 delegates. Mr Sanders, with only 23%, took some 48 delegates, with the rest still to be distributed.
Mr Trump won that traditional battleground state by 1.2 percentage points in the 2016 presidential election.
In Illinois, Mr Biden trounced the left-wing Vermont senator, with a margin of over 20% and at least double the number of delegates.
With most votes counted in Arizona, Mr Biden has a double-digit lead over Mr Sanders in the south-western state.
A Democratic candidate needs 1,991 delegates to clinch the nomination.
On Wednesday, Mr Sanders’s campaign said the senator, who lost the 2016 Democratic nomination following a surprisingly strong performance, will consider his next steps.
“The next primary contest is at least three weeks away. Sen. Sanders is going to be having conversations with supporters to assess his campaign,” Faiz Shakir, the Sanders campaign manager said.
“In the immediate term, however, he is focused on the government response to the coronavirus outbreak and ensuring that we take care of working people and the most vulnerable.”
Prior to Tuesday’s vote, Mr Biden had won in 16 of the last 21 state contests.
The former US vice-president’s triumph last month in South Carolina – his first ever primary win over three campaigns for president – resuscitated his faltering campaign.
What issues mattered to voters on Tuesday?
According to opinion polling, most voters said electability was a priority for them.
About three in four Florida voters said Mr Biden would have a better chance of beating Mr Trump, a Republican. Just one in five said the same of Mr Sanders.
Older voters were more likely to say they supported Mr Biden.
Nearly half of Florida’s voters said Mr Sanders’ stances were too liberal.
How did the two candidates react?
In a webcam speech from his home in Wilmington, Delaware, to comply with US anti-coronavirus advice against public gatherings, Mr Biden appealed to Mr Sanders’ passionate supporters.
He said: “Let me say, especially to the young voters who have been inspired by Senator Sanders, I hear you, I know what’s at stake, I know what we have to do.”
But he focused largely on the outbreak sweeping the US, striking a unifying tone as he said: “The coronavirus doesn’t care if you’re a Democrat or a Republican… we’re all in this together.”
Mr Sanders hosted an online address from Washington DC, but he did not drop any hints about the future of his campaign.
He instead talked about the coronavirus crisis, outlining proposals to address the pandemic, which he said would cost some $2tn.
Game over for Bernie Sanders?
Democrats in three states have just cemented the presidential nomination for Joe Biden.
Bernie Sanders was soundly defeated in Illinois and Arizona and routed in Florida, where in one county he finished third behind Michael Bloomberg, who dropped out weeks ago.
He will fall even further behind in the national convention delegate count, as the primary season appears to be heading towards suspended animation, with multiple states delaying their contests until June.
He is going to face growing calls from Democrats to gracefully bow out – something he did not do until the eve of the convention four years ago, much to the consternation of many Hillary Clinton supporters.
The bottom line for Mr Sanders may be evaluating what’s best for the movement he created.
Will staying in the race give him a continuing platform to talk about his issues and buy him time for a potential comeback?
Or will hanging around only increase the chances that he is relegated to an electoral afterthought?
How else is the coronavirus affecting election season?
Ohio was also due to hold a primary on Tuesday, but it cancelled the vote hours before polls were due to open, putting it off till June.
Voters in the three states that did head to polling stations on Tuesday encountered hand sanitiser dispensers and workers in surgical gloves.
Several other states have postponed their Democratic presidential primaries, including Georgia, Louisiana, Maryland and Kentucky.
The Democratic National Committee blasted Ohio for sowing “chaos and confusion” and urged remaining primary states not to follow suit.
But Puerto Rico, which is scheduled to hold the next Democratic primary on 29 March, is also planning to reschedule.
Party grandees are encouraging states and territories instead to extend postal and early voting to reduce public exposure to the virus.
Who’s getting Secret Service protection?
On Tuesday, the US Secret Service said it would this week begin providing full protection for Mr Biden. His codename will be Celtic, the same as when he was vice-president.
Mr Biden requested the security detail after being repeatedly accosted by protesters on the campaign trail.
Two protesters rushed a stage in Los Angeles earlier this month and came within a stride of the candidate as he gave a victory speech.
Mr Sanders has not made a request for Secret Service protection.