Donald Trump ran through his checklist of conspiracy theories Monday in a rambling conversation with his uber-wealthy supporter Elon Musk that was initially derailed by what the tech titan said was a technical glitch.

In a very one-sided conversation on X, Trump vented about a "zombie apocalypse" of immigration, repeatedly blasted President Joe Biden as "stupid", and mused on developing a new missile defense system based on the one that defends Israel.

The Republican standard-bearer also dismissed climate change, whose sea-level rises he said would simply create more real estate opportunities.

"The biggest threat is not global warming, where the ocean is going to rise one-eighth of an inch over the next 400 years," he told Musk.

"You'll have more ocean front property, right? The biggest threat is not that. The biggest threat is nuclear warming, because we have five countries now that have significant nuclear power, and we have to not allow anything to happen with stupid people like Biden."

What was billed as a "no limits" conversation between the two started more than half an hour late, with many of those logging on unable to listen in live.

Musk, the world's richest man according to Forbes, claimed the platform formerly known as Twitter had experienced a cyber "attack."

Border 'apocalypse'

The conversation was intended to help reinvigorate Trump's stuttering campaign, which has flagged since Biden dropped out of the race, to be replaced by a surging Kamala Harris.

The young men who view Musk as a hero are a prized target for Trump, whose following tends to skew older.

More than a million users listened in live to the conversation on X.

Musk, who has said he previously voted Democrat, has thrown his weight — and his wealth — behind Trump since a gunman tried to assassinate the Republican at a rally last month.

The apparent technical difficulties come after Musk fired swathes of staff at the platform, and also served as an uncomfortable reminder that the Tesla boss had once backed Trump's rival Ron DeSantis, whose campaign launch on the platform was also beset by problems.

When things finally got under way, Musk said the "massive attack illustrates there's a lot of opposition to people just hearing what President Trump has to say."

Trump was banned from Twitter after a mob of his supporters stormed the US Capitol in January 2021, but Musk reinstated him when he took the platform over and renamed it.

The South African-born billionaire has emerged as a major voice in US politics, but is accused of turning X into a megaphone for right-wing conspiracy theories.

He is one of the Democrats' fiercest critics, leveraging his 194 million-strong following on X to assail liberal efforts to boost diversity and inclusion — what he calls the "woke mind virus" — and the White House's handling of the southern border.

"We have people streaming over," Musk told Trump, likening the border to the "zombie apocalypse" depicted in the film "World War Z."

"It's just not possible for the United States to absorb, you know, everyone from Earth," said Musk, identifying himself as a "legal immigrant."

Cost 'cutter'

In his "chat" with Musk, Trump returned often to a favourite theme — boasting about his relationship with autocrats like Russia's Vladimir Putin and China's Xi Jinping, and insisted America would be safer under his stewardship.

"One of the things we're going to do is we're going to build an Iron Dome," he said, referring to Israel's missile defence system.

"We're going to have the best Iron Dome in the world... because it just takes one maniac to, you know, start something."

Musk reiterated his strong support for Trump, saying the ex-president "was the path to prosperity and Kamala is the opposite."

At one point he also appeared to be touting for a job under a future Trump administration, suggesting he would like to serve on a cost-cutting committee.

"I think it would be great to just have a government efficiency commission that takes a look at these things and just ensures that taxpayer money... is spent in a good way," he said. "I'd be happy to help out on such a commission."

Trump appeared sold on the job application.

"You're the greatest cutter," he told the man who slashed swathes of staff months after taking over Twitter.

AFP