No penalty has been applied to faithless electors, partly because such a penalty is unconstitutional. Supreme Court cases US Term Limits v Thornton and Ray v Bl

No penalty has been applied to faithless electors, partly because such a penalty is unconstitutional. Supreme Court cases US Term Limits v Thornton and Ray v Blair make it clear that states cannot force electors to vote in any particular way once elected, though they can require electors to solemnly promise in advance to do so. In practice, electors don't violate those promises unless the promise turns out not to matter. Sometimes an elector will chose to show off by choosing some other candidate to vote for from his promised choice, but always only after checking that it won't affect the final result. Parties pick people that are proven loyal enough over time to be depended on.