Likely the easiest weapon to do it with unless you can get your hands on some C4 or a fuckin RPG or something....
Aaaaand I'm on a list.
But hear me out:
Knife. Hahahaha no fucking way you're getting that close without a security check. I think? I'm not about to try and report back either.
IED: Okay. Decent chance. Where do you put it? The Beast will withstand that (i think?...dunno much about the presidential limo other than the doors are like 8 inches thick.) Detonation must go through, and we all know thats difficult to get right. Timing must be perfect, and it has to be out of sight//out of mind till it goes off.
Gun. Second Amendment makes them pretty easy to get. Long range weapon means you can avoid up close and personal security. Might even get off a few shots with some sort of rifle? (Imma be honest, don't know much about guns.... But you get a good rifle and scope?i think you can hit anyone in a reasonable distance) Multiple shots makes it easier to finish the objective. Bomb is one chance and knife yeah knives...no.
Ammo is also only restricted in a few states (as of recently. was on the ballot in california this election I believe). And guns are easier to conceal than say, an RPG or whatever ordinance one would want in their attempt.
So there you go. I've definitely missed other options like a hellfire missile or a nuke, but what kind of ordinary person has a fucking hellfire missile?
I think a gun is the most likely. Look at most assassinations: MLK gun, Kennedy: gun, Lincoln: Gun, Reagan assassination attempt: Gun, Both roosevelts (FDR and Teddy) Gun, ford: Gun.
The attempts on presidents that havent been through guns have all been foiled before they were carried out. Car bombs and whatnot were found and dealt with and the presidential motorcades were either delayed or diverted depending on the circumstance. Another dude tried to hi-jack a plane and crash it into the WH, but he was not successful. The hijacker took control through shooting the pilot and co-pilot. Again, guns.....