Party coalitions are, of necessity in this country, diverse, broad coalitions, with many sub-segments. If the party leadership itself abandons the coalition, especially in an explicit attempt to deny the Republican nominee a win, it will have lost whatever authority it has remaining to manage the various coalitions.

Moreover, if Trump is to lose, the lesson (assuming there is any) about his popularity would be best learned if he loses straight up. Abandoning the party and running a rear guard action would enable Trump supporters – assuming he loses – to operate under a “stabbed in the back” theory in 2020 and going forward. And they’d be right!

This is the ultimate rejoinder to advocates of “we need someone to save the down-ballot candidates.” Maybe Trump will drag the bottom of the ticket down. But even if a third party candidate managed to save some House and Senate seats (and there’s no guarantee Trump’s supporters wouldn’t skip the down-ballot races in retaliation for a third party bid), it would come at the cost of the party’s long-term future.