Performing at a rally for the Democratic candidate, Springsteen used time between his numbers to argue Ms Harris will protect democracy and fight for women's reproductive rights.

He said he wants a president who "reveres the constitution" and does not "threaten" freedom, taking aim at Mr Trump for not holding those values.

"He does not understand this country, its history or what it means to be American," Springsteen said, adding Mr Trump is "running to be an American tyrant".

Springsteen was followed on stage by former President Barack Obama, who said Mr Trump's "goofy" behaviour "does not mean his presidency wouldn't be dangerous".

He singled out comments from Mr Trump's former chief of staff, John Kelly, who has claimed the former president said he wants his generals to be like Hitler's.

"In politics, a good rule of thumb is - don't say you want to do anything like Hitler. That's just good political advice," Mr Obama said.

"But it is useful because it gives us a window into how Donald Trump thinks. And John Kelly isn't the only one saying this."

Speaking at his own rally in Arizona, Mr Trump accused Ms Harris of having "deliberately dismantled our border".

He said his Democratic rival "threw open the gates... to an invasion of criminal migrants from prisons and jails from insane asylums and mental institutions from all over the world".

He went on to claim people from 181 different countries are coming to the US illegally, adding: "We're a dumping ground. We're like a garbage can for the world."

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Mr Trump has long been criticised for his rhetoric around immigration.

If he wins, he has pledged to launch the largest deportation effort in US history and said at a rally last month deporting migrants would be "a bloody story" - rhetoric that sparked criticism from immigrant advocates.

The election, which will kick off on 5 November, remains a tight race, according to polls, which give Ms Harris a narrow lead nationwide, while bookies appear to consider Mr Trump the favourite.