not for the faint of heart
1) You’ve got to sign up for an account and password.
2) Click on a small gray question mark icon the upper-right hand corner.
3) From there, you’ll be sent to another page with the option to make more contributions. There should be a “Manage” button on the lower left-hand corner. Click on that.
4) You’ll be sent to a separate website run by the campaign vendor, and there should be an option to access “recurring plans.” That should then finally give you an option to cancel payments.
5) But they’ll keep your credit/debit card info anyway until you replace it with another card. There’s apparently no way to delete it from their system.
Canceling donations to the Clinton campaign (who would want to?) is considerably easier.