Donald Trump’s campaign web site provides no way for campaign contributors to cancel recurring donations.
Once you sign up, there is no apparent way to stop giving—unless you cancel your credit card or possibly arrange with your bank to stop payments.
Hillary Clinton’s campaign web site has a “remove” button for those who want to stop payments.
Donald Trump’s web site won’t allow you to cancel recurring donations by Jeremy Stahl for Slate. (Hat tip to Joseph Cannon).