If Trump doesn’t get the Republican nomination, I think he will go 3rd party. Why? It solves best for his ego (which is his sole decision function).
Remember, he will lose either way. The question is which path solves for a more graceful exit (if “graceful” is a word that can be used in a Trumpian context).
Trump will do anything to avoid humiliation. This is why he might actually prefer a 3rd party route. He goes out in a blaze of glory. We fought the good fight. I did my best against a stacked deck. Etc. Etc. If he’s the actual Republican nominee, he’s going to fail spectacularly and embarrassingly. An epic wave of anti-Trump voters coming out. And the mass of suburban lumpen-Republicans staying home – that affluent, well-educated, enclaved, un-attached crowd whose political convictions start (and stop) at “I just don’t want to pay taxes. Especially to pay for [pause, quick look around] those people. Why don’t they just get a job!“*
Trump also loves to be a victim. If he loses at a contested convention, he can plausibly claim he was “robbed.” That becomes the justification for a 3rd party run. Sampson tearing down the temple.
Trump loves the spotlight. There’s no way he’s going to dutifully line up behind the party nominee. He’d prefer to be front and center. Driving the debate. And participating in the actual debates come to think of it. Aieeee! Buy the TV networks! Ratings will be sky high!
The first point is the key point. If Trump gets the nomination, he will go down in history as a spectacular failure. Branded a loser, he also loses any political influence in future years. “Branded a loser” is not a desired Trumpian outcome. So maybe he plays to lose from here? Probably not (he is a delusional megalomaniac after all). But if he loses at the convention, I don’t think he’s going away….