From Brother Charlie Pierce:
...[Republican leaders] know that He, Trump has exposed the dark and beating heart of both modern conservatism and the electoral success of the modern Republican Party. They can no more distance themselves from it totally as they can distance themselves from their own hearts. So they support, but don't endorse, and assume people are too dim to notice that the proposition is absurd on its face.
Splunge (h/t Monty Python) is one of the greatest and least used words of all time. It is a nonsense syllable used by yes-men, toadies and other species of spineless careerist who desperately want to both look decisive and suck up to a boss whose incoherently oscillating opinions and wild mood swings they cannot predict or control.
Note: The Atlantic has a handy cheat sheet on which Republicans have endorsed Trump and which have not.