So, there’s been a few poorly thought out rage attacks.
A guy fired a few rounds in the general direction of the white house. A guy hopped a fence. A guy crashed a small drone.
None of those attacks had even the possibility of harming the President. (even the guy firing rounds didn’t use a bullet had the potential of going through the armor the white house must have. I mean, I don’t know what the glass and walls can take, obviously that isn’t public, but it can’t be any weaker than ordinary armored cars which can take assault rifle intermediate caliber rounds)
You might have a point if a serious attempt that might work were made, or people were caught with the materials and plans for one. That hasn’t yet happened.
What would be an attack that would be a serious attempt?
There are extremely high caliber weapons, not publicly available without special licenses, that might go through the protective armor. (20mm+ armor piercing ammo). The bad guys could build a massive IED that uses explosively formed projectiles, similar to the ones that killed tanks in Iraq. At least once, someone has shaken hands with the president who wasn’t on the guest list - maybe the bad guys could have used an implanted bomb. The bad guys could try hijacking an airliner again. All these things would probably fail, but it’s at least possible the bad guys would get lucky.
The thing is, if you think about it, all these attacks that could potentially harm the President have something in common. They would all require extensive planning, resources, and money. Any person with access to those things might rationally say “wait a moment. I want to harm the President because I don’t like his politics. If he actually dies, then won’t there be a backlash where Congress and the general public elect someone just like the President was in his memory?”
Or, alternatively, “I think the current President is a fool. So let’s put that Joe Biden/Dick Cheney/Al Gore guy in charge instead. That’ll put the country on the right track. Oh, wait…”
That’s the real defense against assassination. As long as the vice president is significantly less popular and competent than the President, there’s no rational reason to harm him.
So you only have the nuts. Firing a few rounds in the general direction of the building or crashing a small plane with no bomb on it into the white house (this happened during the Clinton administration) isn’t going to harm a hair on the big man’s head.