Donald Trump will only be the second President in U.S. history to serve two non-consecutive terms, and the first to do so after the passage of the 22nd Amendment, which provides that a person shall only be elected President twice. It's possible an attempt will be made to remove the constraints of the 22nd Amendment whether through repeal or redefinition by the courts, that it only applies to consecutive terms. This can resolve yes if:

1) A bill is introduced in the US Congress to repeal the 22nd Amendment (regardless of outcome)

2) An op-ed is published in a major newspaper (>100k subscribers), by a current or past federal government official, notable academic, or major media figure, arguing that the 22nd Amendment applies only to consecutive terms

3) A paper is published in a top-20 legal journal (W&L Law Journal Rankings) arguing that the 22nd amendment applies only to consecutive terms.

4) Donald Trump, one of his administration members, or an external advisor specifically and seriously calls for the repeal or redefinition of the 22nd Amendment (and not just that it would be nice if Trump could serve a third term).