Beware of the idea of a donation "returned".
The only way to "return" the money is to not cash the check or not process the credit card charge. If the money has already been accepted it is nearly impossible to "return" the money.

The Clinton campaign in 1996 was caught not vetting checks and some were determined to be illegal contributions. They returned the money by writing checks and sending them back to the contributors. There was never any indication that the checks got cashed. After all, the contributor wanted to send money to the campaign. The campaign already had the money. So why bother cashing the check to get the money back when they didn't want it back. So the Clinton campaign still had the money to use as they wished. They were so blatant about assuming the returned contribution checks would not be cashed that the account on which the checks were issued never had enough money to cover the checks in the first place.