George Santos was utterly triumphant. He had just flipped a Long Island congressional seat, improbably helping deliver Republicans a House majority. It was time for a post-election shopping spree.

Over just a few days last November, Mr. Santos dropped $6,000 at Ferragamo, perhaps partly on the red designer sneakers he later wore to walk the marble halls of Congress. He withdrew $800 in cash at a casino, where aides said he liked to play roulette. He paid off his rent, and he pulled out another $1,000 in spending money at an A.T.M. near his apartment in Queens.

It would have been nothing for the kind of wealthy financier Mr. Santos purported to be on the campaign trail. But that was a ruse. All of it was being illegally funded by Mr. Santos’s congressional campaign, which wired him $20,000 just after Thanksgiving without ever telling campaign donors or the Federal Election Commission.

Those outlays were just a fraction of the tens of thousands of dollars that Mr. Santos siphoned from unknowing donors for years, propping up the kind of glittering consumer dream the 35-year-old son of immigrants never could have afforded himself, according to previously undisclosed bank records and other financial documents released by congressional investigators on Thursday.

Among the bills footed by campaign donors: trips to the casinos in Atlantic City and an exclusive Hamptons enclave; $4,127.80 in purchases at the French fashion house Hermès; regular cosmetic treatments labeled “Botox” on internal campaign records; and even small purchases on OnlyFans, a platform where some participants charge money for explicit content.

The bipartisan House Ethics Committee report tallying them up went even deeper, unveiling new details and confirming news stories by The New York Times and others about a tangled knot of biographic fictions, business frauds and bizarre campaign schemes that federal prosecutors are also scrutinizing.