Last February, the billionaire financier Nelson Peltz summoned a group of about 20 wealthy, predominantly Republican donors and a handful of G.O.P. strategists to dinner at his $334 million waterfront estate in Palm Beach, Fla. There were plenty of people in the room who had publicly disavowed former President Donald Trump after the Jan. 6 insurrection at the Capitol — Peltz among them — but it was pretty clear now that he was going to be the candidate, and it was time to get onboard and figure out how to help him win. There were a lot of problems. An especially uncomfortable one was that a lot of donor money was going to paying Trump’s mounting legal bills rather than building a serious political campaign.

Peltz, who was 81 at the time and made his fortune via junk bonds and leveraged buyouts, had gathered some traditional high rollers, including the hedge-fund manager John Paulson and the Las Vegas casino tycoon Steve Wynn, as well as Ronna McDaniel, then the chair of the Republican National Committee. He had also invited Elon Musk.

For much of his career, Musk gave modestly to candidates of both parties. He was drawn to President Barack Obama, making several visits to meet with him in the Oval Office and inviting him to Cape Canaveral to see SpaceX’s Falcon 9 rocket. But he didn’t really like spending time with politicians, and never aspired to be a political power broker, at least in the traditional sense. His business empire spanned the globe, and administrations everywhere came and went. He seemed to view himself as being bigger than any party.

In the years since the 2020 election, though, Musk had been following a number of his friends in the tech industry — some dating back to his earliest days in the business, when he helped found the company that became PayPal — on a journey to some of the more baroque regions of the far right. He was becoming increasingly outspoken about his views but had less to say about the daily scrum of partisan politics. He had quietly given more than $50 million to fund advertising campaigns attacking Democrats in the 2022 midterms, The Wall Street Journal has reported, and in 2023 he donated $10 million to an outside group that helped fund the presidential bid of Gov. Ron DeSantis of Florida. Now he seemed open to doing a lot more.

Peltz gave Musk the honor of speaking first. He told the group that he had always been a Democrat, but no longer. And, despite being new to political campaigns, he had some ideas to share. What worked with his electric car company, Tesla, he said, was not paid advertising but word of mouth. If everyone in the room told two friends to vote for Trump — and told them to tell two friends — he would win. Then Musk underscored what he saw as the real stakes of the presidential race.

Musk was born in South Africa, became a Canadian citizen and once admitted that his immigration status was in a “gray area” when he founded his first company in the United States. But in recent months, he became obsessed with a conspiracy theory that Trump and his followers were promoting: that Democrats were allowing immigrants to pour into the country to create more Democratic voters, in effect stealing the election. In the months leading up to the gathering at Peltz’s home, Musk helped spread the idea — a central plank of MAGA’s election denialism — across his own social media platform, X. (Musk did not respond to a detailed request for comment.)