Joe Biden could seize the number of delegates needed to formally clinch the Democrats’ presidential nomination on Tuesday as seven states and the District of Columbia push through a pandemic and exploding racial tensions to host the largest slate of primary elections in almost three months.

Voters are navigating curfews, health concerns and a sharp increase in postal balloting as elections take place from Maryland to Montana.

Four states were originally scheduled to vote in April but delayed their contests because of the Covid-19 outbreak.

Pennsylvania offers the day’s biggest trove of delegates and represents 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.

“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.”

Mr Biden needs to win 89% of all delegates at stake on Tuesday to clinch the nomination, but his role as his party’s clear presidential nominee is not in danger should he fall short.

With a dominant showing on Super Tuesday in early March, the former vice president pushed out all his major opponents.

He will almost certainly secure the needed delegates later in the month if necessary.

Tuesday offers 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.

Donald Trump and Joe Biden will duel for the keys to the White House in November (Patrick Semansky/AP)
Donald Trump and Joe Biden will duel for the keys to the White House in November (Patrick Semansky/AP)

Vermont Senator Bernie Sanders is not actively campaigning, having suspended his operation and endorsed Mr Biden, but his name is appearing on the ballots.

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.

It is much the same in Philadelphia, where officials have promised that voters would not be arrested should their city’s 6pm curfew be extended for a fourth consecutive night.

“We are in unique times and voting is a unique challenge for people,” said Josh Schwerin, chief strategist for the pro-Democrat super PAC Priorities USA.

President Donald Trump (Patrick Semansky/AP)
President Donald Trump (Patrick Semansky/AP)

He said that his organisation and others will be watching closely “to see how well it works, where issues are, and where obstacles have been put in place”.

Political groups have had to adjust as some states move to a system that relies largely on voting by post.

They include Montana, where all 56 counties decided to vote entirely by mail.

Voting rights watchdogs in multiple states have expressed concerns about access to mail ballots, confusion about deadlines and a shortage of poll workers that could lead to long lines.

Those voting on Tuesday include the District of Columbia, Indiana, Maryland, Montana, New Mexico, Pennsylvania, Rhode Island and South Dakota.

An eighth state holding primary elections, Iowa, chose its presidential nominee early in the year and focused on other offices.