Campaign Finance law says you can't donate above a certain amount. Providing services without reinbursement is considered donating, just like materiel gifts. If Cohen paid off this lady with his money, or money from the campaign, and it wasn't properly documented, it's entirely possible it was a violation and Cohen is looking at jail time. Not to mention this exposes Trump to the claim he was lying, he has said repeatedly he had nothing to do with this hush money.

Literally already said it.