I don’t think it would prompt some kind of vindictive vote. That side of it is only going to energize those who were vehemently republican anyway. Republicans would hammer on any and all sympathy they can eke from having their candidate assassinated (regardless of the truth they will say it was the left, and at best people will think the guy was just crazy), and the average person only half paying attention will eat it up. Dems would be even more hamstrung in their rhetoric against the GOP considering the gravity of an event like that. Even with that aside, they’re now running Joe Biden against whichever face the GOP tells their voters to line up behind – who you can bet will be all in on the kind of stuff that will do even more lasting damage to our country. Biden is not a strong candidate, and without the uniquely unlikable personality and character of Trump I’m not sure there’s enough motivation amongst voters to carry him to another term.
But all of that was a lot to type, so I just said it would give them a massive boost