You're assuming that Trump will not try to stay on as our dictator.

No, I'm assuming that even if he tried he'd fail. Though I don't think there's any likelihood at all that he'd try. He's far too risk averse - he's never made a big gamble with his own money (and certainly not with his own life) on the line. He knows he doesn't have what it takes to seize and hold power without the benefit of the rule of law. Even in extremis, all he did was try to get other people to take all the risks and do all the work give him the power he wanted. He knows full well that if he tried to seize power openly outside of the law, rather than trying to weasel around inside the law, someone would "usurp" him within the year. Weak dictators never last - they invariably end up put against the wall by someone who is genuinely adept at ruthlessly seizing power and willing to risk everything to get it.