The election odds cited by Mr. Trump came from a crypto-powered gambling website called Polymarket. Using digital currencies, gamblers on Polymarket have wagered more than $100 million on the outcome of the presidential race, turning the site into the internet betting phenomenon of the 2024 election.

Elon Musk has promoted Polymarket’s odds on X, calling them “more accurate than polls, as actual money is on the line.” CNN and other news media organizations have featured the projections in their election coverage. And as the market has swung heavily in Mr. Trump’s favor, he has relentlessly publicized the site’s numbers, seeking to create a sense of inevitability about the election’s outcome.

“A gambling poll, as they call it,” Mr. Trump said recently of Polymarket. “I don’t know what the hell it means, but it means that we’re doing pretty well.”

But Mr. Trump’s apparent lead may be an illusion. The odds on Polymarket began favoring him this month after just four accounts, with user names like Fredi9999 and PrincessCaro, bet more than $30 million on a Trump victory, according to an analysis of transaction records by Chaos Labs, a crypto data provider. Polymarket said on Thursday that all four accounts were controlled by one person, whom it described as a French national with a financial services background, without revealing the person’s identity.

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For much of the fall, Polymarket’s odds suggested that Mr. Trump and Ms. Harris were locked in a tight race, mirroring the polls. Then the odds diverged substantially this month, after the four accounts placed large bets on the former president.

On Oct. 11, Mr. Trump posted a screenshot of Polymarket that showed he had a 55.5 percent chance of winning the election. On Monday, he posted a new screenshot showing that his chances had increased to 64 percent.