Joe Biden scored a clean sweep of the seven US states conducting Democratic presidential primaries on Tuesday, just hours after slamming the “narcissism” of Donald Trump.
The delegate haul from the elections is important to Mr Biden’s goal of gaining enough delegates to claim the Democratic nomination before the party’s summer convention.
The results on Tuesday may leave the former vice president just short of the 1,991 delegates he needs, but primaries next week in Georgia and West Virginia could put him over the top.
Also choosing a nominee on Tuesday were voters in the District of Columbia, where results are pending.
Voters had to navigate curfews, health concerns and a sharp increase in postal balloting, with four of the states originally scheduled to vote in April but forced to delay their contests due to the Covid-19 outbreak.
Pennsylvania offered the day’s biggest trove of delegates and represented a high-profile test case for Republicans and Democrats working to strengthen their operations in one of the most important general election battlegrounds.
“We think we’re prepared,” said state Democratic Party chairwoman Nancy Patton Mills earlier on Tuesday.
“Thank goodness we have the opportunity of working this out in the primary because we don’t know where we’ll be with the pandemic in November.”
With a dominant showing on Super Tuesday in early March, Mr Biden has already pushed out all his major opponents and is almost assured of securing the required delegates later in the month.
Tuesday offered a historic opportunity for the 77-year-old Democrat, who is waging his third presidential campaign and who hopes to amass as many delegates as possible to show strength before going up against President Donald Trump.
On the eve of Tuesday’s primaries, senior adviser Jeff Weaver encouraged progressives to vote for Mr Sanders anyway.
“People who support Bernie Sanders and his agenda, who want to maximise the influence of progressives at the convention, should cast their vote for Bernie Sanders,” Mr Weaver said, reminding voters that the Vermont senator is seeking leverage to shape the party’s platform and rules.
The comments serve as a reminder that Mr Biden may have no legitimate Democratic rivals remaining, but he must still win over sceptical activists from his party’s far-left flank who worry he is too close to the political establishment.
Party unity will likely be an afterthought this week, however, as more immediate health and safety concerns dominate the national conversation.
The coronavirus death toll has surged past 100,000 nationwide, and thousands of new cases are reported each day.
At the same time, several major cities, including some voting on Tuesday, are grappling with protests following the killing of George Floyd, a handcuffed black man who died after a white Minneapolis police officer pressed his knee into Floyd’s neck for several minutes.
Washington DC mayor Muriel Bowser ordered a 7pm curfew, though voting places will be open until 8pm.
Voting has been deemed essential, and city officials say voters will not be subject to arrest if they cast ballots during the curfew.