In 2016, as his presidential campaign was struggling for funds and his last big lender, Deutsche Bank, unexpectedly turned him down for a loan, Trump received a sudden windfall of $21 million, according to a New York Times analysis of his leaked tax returns. The highly unusual one-off payment came from the Las Vegas hotel Trump owns with casino mogul Phil Ruffin, and was routed through several Trump-controlled companies and paid in cash. The tax records don’t show what the $21 million was used for, but Trump contributed $10 million to his campaign as its fortunes waned. If the $21 million wasn’t for actual business expenses, it would have been illegal for Trump to claim the payment as a tax deduction. If it went to his campaign, it could be considered illegal campaign contributions, the Times reports.

“Why all of a sudden does this company have more than $20 million in fees that haven’t been there before?” tax professor Daniel Shaviro told the Times. “And all of this money is going to a man who just happens to be running for president and might not have a lot of cash on hand?” White House spokesperson Judd Deere said Trump was longtime partners with Ruffin “and earned whatever payments he received.”