The term "Faithless Electors" describes those electors who have voted against the wishes of their states. Some states have laws on the books prohibiting this, others do not. Even those states who prohibit it have various untested consequences. I do realize that the chances of this happening are almost nil, but in 1836 Virginia's 23 electors conspired to vote against the VP nominee which threw the election of the VP to the senate where he was elected anyway. For the electors to vote against their state's election would require extraordinary circumstances which I do not think we are even close to. But, technically, it is possible.