I think Trump has regretted becoming President from the moment he knew he had won on election night. I don’t think Trump thought he had any more chance of winning than anybody else did, which is to say unlikely in the extreme. Trump probably understood winning would have consequences, but I don’t think he really understood them. Trump is not someone who carefully thinks through the possible consequences of his actions. It can be taken for granted Trump knew there would be consequence, because at least Cohen, and his Chief Financial Officer Allen Weisselberg would have sat him down and explained to him that even running for President was drawing a dangerous amount of attention to himself, let alone winning. Given how Trump has historically gone about doing business, he can not afford close scrutiny.
I think on one level Trump is loving being President, it is the ultimate ego boost, he probably likes the pomp and ceremony. although the fact he has to go to Paris to get a military parade, with real tanks and missiles must be driving him nuts. He isn’t enjoying the constant mockery, he hates that everybody is always critical of everything he does, he hates the complexity of a job he can’t get his head around, and he really hates that he can’t just order everybody about. I wouldn’t be at all surprised if he really did believe he would be able to lock up Hillary with no more processes than an executive order.
Add to all that he has the Mueller investigation, the New York’s Southern District investigation. He’s lost his compliant congress, come January Congress is going to be making his life miserable, and I think you can expect to see these investigations multiplying. Plus all his old business colleagues are going to be turning on him, Cohen already has, and Allen Weisselberg probably has as well.
At some point, if he isn’t already, Trump is going to be thinking that the only way he can survive this is to follow in Xi Jinping’s footsteps and make himself President for life, Trump’s problem he is not even remotely in Xi Jinping’s league. Trump has surrounded himself with the foolish, the greedy, and the outright stupid. The problem is that Trump is stupid enough, and perhaps desperate enough he might conceivably try it. If that day ever does come, the opportunists, and grifters will savage each other getting to the exits, the real danger for Trump and the office is going to be in the fools he has surrounded himself with. While what in effect would be an attempted coup will have zero chance of ever actually working, and it would probably end up having all the elements of a farce, the precedent could still end up being very damaging.
So yes I would put good money on the fact that Trump spends a lot of his time feeling sorry for himself, and wishing that he gotten a handful less votes in the right places. Maybe he even wishes he hadn’t taken that ride down his golden elevator.