Pete Buttigieg has come under immediate pressure to quickly endorse Joe Biden after announcing the end of his own campaign for the Democrat presidential candidacy.

Party moderates are said to be “desperate” for the former mayor of South Bend, Indiana, to throw his weight behind the vice-president, who is seen has having the best chance of closing the gap on socialist frontrunner Bernie Sanders.

Mr Buttigieg, the first openly gay candidate to make a competitive run for the US presidency, dropped out of the race on Sunday after Mr Biden’s decisive victory in the South Carolina primary.

He told supporters it was time to “step aside and help bring our party and our country together,” adding in a pointed dig at Mr Sanders that “we need leadership to heal a divided nation, not drive us further apart”. An adviser told Reuters that Mr Buttigieg had called time on his campaign to avoid helping the odds of the veteran Vermont senator.

Mr Buttigieg stopped short of endorsing any of his ex-rivals in his departing speech, but he and Mr Biden were reported to have exchanged voicemails on Sunday night, and his decision to pull out of the race has prompted new pressure on the party’s moderate wing to coalesce behind the former vice-president.

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“Dem establishment types in DC want Pete Buttigieg to quickly endorse Joe Biden,” said political analyst Howard Fineman. “They’re desperate to get behind Joe; they think he’s only one who can stop Bernie Sanders. Not that Pete has much clout, but insiders are pushing him hard tonight.”

A Democrat official told The New York Times that Mr Biden had asked for Mr Buttigieg’s endorsement when they spoke on Sunday night. The former mayor indicated he would consider request and told his own team he would sleep on the decision, according to aides, some of whom are said to want him to quickly back Mr Biden.

The official said Mr Buttigieg had also spoken to Barack Obama on Sunday night. The former president is not believed to have specifically encouraged him to endorse Mr Biden, but reportedly asked him to consider how to best use his influence.

Twenty-six per cent of Mr Buttigieg’s supporters would opt for Mr Biden as their second choice – the same number as Mr Sanders, according to recent polling by SurveyUSA.