The sheer magnitude of the money involved is staggering for politics. In the final two and a half months of 2020, the Trump campaign, the Republican National Committee and their shared accounts issued more than 530,000 refunds worth $64.3 million to online donors. All campaigns make refunds for various reasons, including to people who give more than the legal limit. But the sum the Trump operation refunded dwarfed that of Joseph R. Biden Jr.’s campaign and his equivalent Democratic committees, which made 37,000 online refunds totaling $5.6 million in that time.

The recurring donations swelled Mr. Trump’s treasury in September and October, just as his finances were deteriorating. He was then able to use tens of millions of dollars he raised after the election, under the guise of fighting his unfounded fraud claims, to help cover the refunds he owed.

In effect, the money that Mr. Trump eventually had to refund amounted to an interest-free loan from unwitting supporters at the most important juncture of the 2020 race.