At a private fundraising event last summer, Donald Trump launched a foul-mouthed tirade about undocumented immigrants and said that if Kamala Harris wins, this "may be the last election we ever have." A 12-minute audio clip of the Republican presidential nominee's speech was obtained by The Guardian.

The speech was delivered on August 10 in Aspen, Colorado, during a dinner where guests were asked to donate anywhere between $25,000 and $500,000 per pair.

Trump devoted most of his address to border security and immigration, recycling xenophobic claims now familiar from his rallies. “Radical leftwing lunatics” want people to come in from prisons, mental institutions and insane asylums, he asserted without evidence, adding that the US was harbouring “a record number of terrorists”.

The former president insisted that “smart, very streetwise” leaders of Venezuela and other South American countries were sending murderers and drug dealers to the US to reduce their own crime rates, relieve the burden on their prisons and save money.

Trump cited a false example of 22 people he claimed had come to the US after being released from prison in the Democratic Republic of the Congo. “We said, ‘Where do you come from?’ They said, ‘Prison’. ‘What did you do?’ ‘None of your fucking business what we did.’ You know why? Because they’re murderers.”

The candidate added, “I hate to use that foul language”, apparently recognising that his use of the F-word went further than his campaign rallies. The Congolese government has said there is no truth to Trump’s statements.

The candidate went on: “These are the toughest people. These people are coming in from Africa, from the Middle East. They’re coming in from all parts of Asia, the bad parts, the parts where they’re rough, and the only thing good is they make our criminals look extremely nice. They make our Hell’s Angels look like the nicest people on earth.”

Studies show that immigrants are less likely to commit crime than native-born Americans.

Trump flew to Aspen on a Gulfstream G-550 jet once owned by Jeffrey Epstein, the late disgraced financier and convicted sex offender, after his own private plane – a Boeing 757 known colloquially as Trump Force One – encountered engine trouble.

The dinner was held at the $38m home of the investors and art collectors John and Amy Phelan. Guests included the casino mogul Steve Wynn, billionaire businessman Thomas Peterffy, Texas governor Greg Abbott, Florida congressman Byron Donalds, Colorado congresswoman Lauren Boebert and former Colorado senator Cory Gardner.

Trump, who instigated an attempted coup on 6 January 2021 and has claimed that his Democratic rival Harris poses the true threat to democracy, used the exclusive event to warn of dire consequences if she becomes president.

“Look, we gotta win and if we don’t win this country’s going to hell,” he said. “You know, there’s an expression, this could be the last election we ever have and it’s an expression that I really believe, and I believe that this could be the last election we ever have.”

The ex-president was speaking a month before his first and probably only televised debate against Harris, of which opinion polls and pundits would widely judge her to be the clear winner. That was not what he predicted.

“I’m telling you we have a radical left person that’s going be president – if she wins it’s going to be a disaster – she wants to be president very badly. Thank God she’s supposed to be horrible at debating, although she’s nasty, and she’s supposed to be really bad at interviews. She can’t do an interview.”

Trump also claimed that Harris supports the “defund the police” movement, suggesting that she was a typical politician who will revert to type once she is elected.

“Her policy is defund the police. She wants to defund the police. She wants open borders. With a politician – and I’ve seen it because I’ve been on both sides of politics for a long time; now, a short time for this side but I was always a contributor – she wants to go out and she wants to defund the police. And they always go back to their original plot. They always do.”

Harris, a former courtroom prosecutor, did voice support for the “defund the police” movement in a radio interview in June 2020 but later reversed her position after becoming Joe Biden’s running mate.

Trump also reflected on surviving an assassination attempt at a July rally in Butler, Pennsylvania, where 20-year-old Thomas Crooks opened fire from a rooftop, killing firefighter Corey Comperatore, 50, and injuring two other Trump supporters.

Trump told how members of his Florida golf club, Mar-a-Lago, asked to make a contribution to Comperatore’s family. “I said absolutely and they gave me a cheque for a million dollars. That’s a lot of money. Maybe even more impressively we put out a GoFundMe and we raised more than $6m for the group that got hurt, which is essentially three people.”

Then, recalling a meeting with Comperatore’s widow, Helen, he made a risky attempt to find humour in the tragedy. “So they’re going to get millions of dollars but the woman, the wife, this beautiful woman, I handed her the cheque – we handed her the cheque – and she said, ‘This is so nice, and I appreciate it, but I’d much rather have my husband.’ Now, I know some of the women in this room wouldn’t say the same.”

As dinner guests erupted in laughter, Trump quipped: “I know at least four couples. There are four couples, Governor [Abbott], that I know and you’re not one of them. At least four couples here would have been thrilled, actually.”

The event is understood to have raised $12m for Trump’s campaign but was not enough to prevent Harris raising more than four times as much as her opponent in August, the first full month of her bid for the White House.