Sandra, if I revealed my secret ex-librarian powers I'd have to ...

Nope, I copied a phrase you wrote and added Doonesbury to the beginning and Googled it:

Doonesbury Trump can't become President again as he has already been elected twice


MaJoC, I think that instead of "if he says it often enough, he'll start to believe it himself", it's more likely to be "the voters will believe it" because I think he believes everything he says about himself, at the time that he says it, even if he contradicts himself a couple of minutes later.