He should extract a pledge from the rest of the GOP to support him if he is the nominee.
And that is the key.
Like him or not, Trump is well ahead in the polls. The GOPe wants him to lose, and they are going after him more than Hillary.
So at this point, Trump is in an interesting position. Stay, and let them try to smash him. Go third party, and smash the election himself.
Good idea, bet he thought of that.