Ineligible Presidential Electors

The Constitution imposes some qualifications for presidential electors. They cannot be sitting members of Congress. They cannot hold "an Office of Trust or Profit under the United States." And they cannot have violated Section Three of the Fourteenth Amendment.

Suppose that an elector is challenged on one of these grounds. Who decides if the elector is ineligible? While this question was raised in some past presidential elections, no clear answer was ever given. Maybe the Joint Session of Congress is the judge. Maybe it's the other electors from the state in question. Or maybe it's state law as applied by state courts. All three of these alternatives were proposed.

Let's hope this issue is not presented in the coming months.