I'm pretty sure Trump only wants to be President because, well, he wants to be President. So, having achieved this improbable feat, I'm sure he would find it quite easy to slip into the role of figurehead for a Republican Congress, with a few concessions here and there on style, and possibly on his signature issues of trade and immigration. This is essentially what was proposed in his attempted rapprochement with Kasich in order to get the latter to join the ticket. If he does go off the wall, his dearth of committed support amongst the Republican Congressional Caucus will be enough to check any unwise decisions.
Mexico had an example of this. His name was Antonio Lopez de Santa Ana. He would become president, then resign in favor of his vice-president, then come back, and on, and on, and on. Eventually, he lost half of Mexico to the US.
