Joe Biden has swept to victory in Florida, Illinois and Arizona, increasingly pulling away with a Democratic presidential primary upended by the coronavirus.
Mr Biden’s clean sweep also built further pressure on his only rival Bernie Sanders to abandon his campaign.
The former vice president’s third big night in as many weeks came amid tremendous uncertainty as the Democratic contest collides with efforts to slow the spread of the virus.
Polls were shut in Ohio, and although balloting went ahead as scheduled in the three other states, election workers and voters reported problems.
Mr Biden’s trio of wins doubled his delegate haul over Mr Sanders, giving him a nearly insurmountable lead.
On Wednesday, Mr Sanders’ campaign manager said he “is going to be having conversations with supporters to assess his campaign”, but suggested Mr Sanders is in “no hurry to make any decisions about leaving the race”.
Top Democratic leaders and donors have increasingly lined up behind Mr Biden as the best option to square off against President Donald Trump in November.
Using a livestream to address supporters from his home state of Delaware, Mr Biden seemed ready to move past the primary. He paid tribute to Vermont senator Mr Sanders for advancing key issues like affordable health care and combating climate change.
“Senator Sanders and his supporters have brought a remarkable passion and tenacity to all of these issues. Together they have shifted the fundamental conversation in this country,” Mr Biden said.
“So 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.”
With the exception of North Dakota and the Northern Mariana Islands, Mr Sanders has not scored a victory since Super Tuesday on March 3.
He made no immediate move on Tuesday to contact Mr Biden, Democrat sources said. During remarks early in the night, Mr Sanders said little about the future of the race and instead focused on the coronavirus outbreak.
Mr Trump, meanwhile, formally clinched the Republican presidential nomination after facing minimal opposition.
But most action was on the Democratic side, where higher vote totals in some key states suggested enthusiasm that even the coronavirus could not contain. Turnout in Florida’s Democratic primary surpassed the 1.7 million who cast ballots four years ago.
Mr Sanders’ path to the nomination is quickly narrowing, and some Democrats are calling on him to drop out in the name of party unity.
Mr Biden maintained strength on Tuesday with African Americans and older voters who have been the hallmark of his campaign. He also appeared to chip away at Mr Sanders’ previous advantage with Hispanics that helped him win Nevada and California early in the race.
The public health and economic havoc wreaked by the coronavirus will nonetheless influence how the presidential contest unfolds.
As we continue to fight for universal health care and paid leave, it has never been more important to strengthen the trade union movement. Workers must have the right to collectively bargain for better pay, stronger benefits, and more power over their lives.— Bernie Sanders (@BernieSanders) March 17, 2020
Rallies and other major events have been cancelled.
Democratic National Committee chairman Tom Perez urged states with forthcoming primaries to expand vote-by-mail and absentee balloting, as well as polling station hours — trying to ensure the primary is not further hampered.
But the damage may have already happened.
Four states — Louisiana, Georgia, Kentucky and Maryland — have joined Ohio in moving to push back their primaries, and others may yet do so.
That has left the Democratic primary calendar empty until March 29, when Puerto Rico is scheduled to go to the polls, but island leaders are working to reschedule balloting there too.
That means there is nowhere for Mr Sanders to gain ground on Mr Biden any time soon, even if he could find a way to mount a sudden surge.
Politicians on both sides expressed frustration on Tuesday after Ohio’s primary was postponed until June by the state’s elected officials.
The Ohio Democratic Party lodged a lawsuit on Tuesday afternoon over secretary of state Frank LaRose’s decision to set a new date, saying that power rests only with the state’s legislature.