They have tried killing him numerous times. But /our guys/ have been 5 step ahead, thank GOD.
First they tried poisoning his diet Coke tank they had installed in the Whitehouse. When he got sick, Melania noticed, and started buying him random Coke cans from random stores herself.
2) They tried shooting AF1 out of the sky on his first "public" trip to Asia. Missile came out of a sub in that Washington State waterway or sound, I think they called it. We got nice missile pic from Q, and a hint about habbenings.
3) numerous people have attempted break into the Whitehouse grounds
4) Last rumor I heard caused him a trip to the doc from alleged food poisoning episode, but, this was not verified.
These are just the ones I have in memory.
There is a Q post that asks what would happen if the NSA had texts showing certain people were actually texting about various assassination plots, so there is that. Might rear it's ugly head in some trial or grand jury. Who knows what those plans would have been.