A US election featuring Donald Trump and Kamala Harris would give voters “a choice between the prosecutor and the criminal”, a Democratic Party group has said.

Vice president Ms Harris is the frontrunner to be the Democratic nominee for the US presidential election in November, after president Joe Biden dropped his re-election bid following concerns within the party that he would be unable to defeat Republican nominee Mr Trump.

A spokesperson for Democrats Abroad has described Ms Harris as an “energising factor” in the wake of Mr Biden’s resignation.

John Scardino, a spokesperson for Democrats Abroad, told the PA news agency that he believed Ms Harris would unite America.

Mr Scardino said: “She’s a hard worker. She is incredibly intelligent and I do think she is going to be out there campaigning like crazy to get every vote that she possibly can.”

He added: “If she becomes the nominee, then voters have a choice between the prosecutor and the criminal in the November election.

“And I think that really draws an appropriate and stark contrast between what the Democrats are offering and what the Republicans are offering.

Republican presidential candidate former president Donald Trump speaks at a campaign event
Trump aides had wanted Joe Biden to remain in the race (Carlos Osorio/AP)

“I think that there is a lot of excitement about her as the potential nominee.”

Ms Harris is the first woman, black person and person of South Asian descent to serve as vice president.

If she becomes the Democratic nominee and defeats Mr Trump in November, she would be the first woman to serve as president.

Mr Scardino said that this “sends a message … to some voters who may not have been as enthusiastic about the choices in the election, that this may be somebody that they feel may be more sensitive to their issues”.

“So I think it’s an energising choice. I think that Kamala Harris as a candidate can be a real energising factor,” he said.

He added: “I think Kamala Harris, in carrying forward a lot of the programmes that Joe Biden has set in motion, could potentially appeal to a lot of those voters who feel disaffected by the Republican Party led by Donald Trump.”

Mr Biden said on Sunday that choosing Ms Harris as his running mate was “the best decision I’ve made” and endorsed her as his successor.

Mr Scardino added that he believed Ms Harris had the “opportunity” to be “a unifier”.

He said: “In the last 24 hours since Biden announced that he was stepping down … there’s 100 million US dollars that has been donated to Democratic candidates. And of that, about half has gone to Kamala Harris.

“These are record-breaking amounts … it is an indicator of where support may lie. So when you look at the amount of support that has flooded into not only supporting Kamala Harris, but I think Democrats in general, (it is) a very good indicator of her, of the opportunity that she has to be a unifier.”