I have fathomed what Donald Trump is up to.
He does not want to be president of the United States, and never did.
When he declared his candidacy, it was a goof, a stunt intended to draw attention and perhaps set up an audience for whatever his next reality show would be.
Then, to his dismay, his candidacy caught on and he began demolishing the serious candidates (to the extent that any of the crowd that ran this time could be considered serious). So he said ever more outrageous things, and it only increased his popularity and demolished more opponents.
Now he is headed straight to the Republican nomination. He can't quit at this point, and he knows he has no business being president. His only recourse is to grow more outrageous, saying things so outré as to guarantee he will lose the election in November.
It's his only way out.