"No person shall be elected to the office of the President more than twice, and no person who has held the office of President, or acted as President, for more than two years of a term to which some other person was elected President shall be elected to the office of President more than once."
So, since Obunghole was elected twice, he cannot serve again as President.
(Since Trump was elected ONCE, for one term, I take it to mean he CAN be elected to one more term.)
That only says he can’t be reelected again. I don’t think that prevents him from taking over from someone else for a period of two years or less. Taking over as the VP doesn’t mean he’s reelected.