A third party will be composed of politicians. they will be offered lifetime wealth and copious funding for re-election campaigns if they play the PC game. They will cave at the same rate as the Republicans cave. That is somewhere above 80%. At this stage of the Oligarchy one party or two parties or three or a hundred and sixteen makes no difference.
What we are seeing now, and I think Trump saw this a few years ago, is a systemic failure of our very form of government.