Former US Vice President Joe Biden has crossed the threshold for the Democratic presidential nomination, locking up a contest for the White House with incumbent President Donald Trump.

Biden has effectively been his party’s leader since his last challenger in the Democratic primary, Bernie Sanders, ended his campaign in April.

But Biden pulled together the 1,991 delegates needed to become the nominee after seven states and the District of Columbia held presidential primaries Tuesday.

The estimate came as Biden swept through primaries in seven states and the District of Columbia.

Biden reached the threshold three days after the primaries because several states, overwhelmed by huge increases in mail ballots, took days to tabulate results.

Late Friday, Biden said in a statement, “It was an honour to compete alongside one of the most talented groups of candidates the Democratic party has ever fielded — and I am proud to say that we are going into this general election a united party”.

This year’s presidential election comes at a time when the US is plagued by the coronavirus pandemic that has frozen the national economy, and, more recently, when nationwide protests against racial injustice have persisted for over a week following the killing of George Floyd, an unarmed black man, under the custody of white police in Minneapolis.

“The country is crying out for leadership. Leadership that can unite us. 9Leadership that can bring us together,” Biden said.

Last month, Biden won Hawaii’s Democratic presidential primary.

The Democratic National Committee earlier postponed the party’s presidential nominating convention in Milwaukee, Wisconsin, to August 17, the week before the Republican Party’s convention, scheduled for August 24 to 27 in Charlotte, North Carolina.

Earlier, Trump’s re-election campaign said in a statement that Biden has “had to adopt most of Bernie’s agenda” — policies that Trump has branded socialist.

But in a series of polls conducted in April, Biden leads Trump in head-to-head general election matchups by an average of 5.9 percent, according to the RealClearPolitics website.

The 2020 US presidential election is scheduled for Tuesday, November 3.

(With inputs from agency)