If this happened the Senate and the Supreme Court let it stick. I would be supremely disappointed with the United States and lost all respect for it if Trump, Pence and a few Republicans WEREN'T assassinated for doing so as that would be an insult and a disgrace to everything this nation stands for and to call it treasonous would be an understatement.
If they attempted that, the Republican party and the Supreme Court better stand up and show some damn back bone. Screwing this nation and allowing them to do that and the precedent it would set and allowed to stand, this nation would basically be in collapse as anything worth having at that point as Democracy is officially dead and any even semi-intelligent dictator wannabe already has everything in place he needs to take over entirely.