The question had already been answered.
The point of the question was to single Trump out from everyone else and set him apart as an outsider from the start.
It was no different then attempting to kneecap a race horse with a steel pipe right out of the starting gate.
But it didn’t work, because a great many people now view themselves as outside and apart from the GOP.
That is the perception but not the reason
The question was the 800 pound gorilla in the campaign and was paramount to the debate. It had to be asked and to be answered.
Trump made the negotiating gambit to not rule out a third party run. He did that because there are elements in the Republican party that are out to kill him. His gambit effectively stopped that effort.
He was shown by Bret to be serious and not blowing smoke on the subject. It is now a dead issue unless the GOPe continues to try to get rid of him and witholds party support.
He is not leaving the Party. The party or at least part of it are attempting to leave him. They now know with certainty that is a very bed choice.
Trump does what he does best...... he made a deal.
Brett gave him the platform to make it