[buwaya]

It’s partly:
BS for votes;
McGuffins for power;
Negotiations for a deal;
Getting in front of a bandwagon that was just waiting for its majorette;
Genuine conviction, after a change of mind;
Deciding that the balance of practicality has moved, and that the new policy, formerly absurd, may be achievable after all;
Politicians minds are squirmy, mutable things, loaded with mixed motives, calculations, negotiations, fears, and every other human weakness.
That’s reality of politics. There are no saints and holy heroes, and even out of politics, most saints and heroes have grave flaws apparent upon close, disinterested examination.

[grey_whiskers]

Maybe he sees the possibility of securing the top spot in prosecution of Hillary and her cabal for Treason.

Trump couldn't promise him that, since such is explicitly illegal -- promising employment in return for political support.