I just mean getting a battalion sized formation of right-wing extremists and disgruntled ex-servicemen together to bum rush the White House and take hostage/kill the president.
Also Olympus Has Fallen apparently.
That said, I'd be surprised if the USSS doesn't have a contingency plan for something like that. I mean, they're basically paid to be as paranoid as possible about the President's safety while still allowing him out of a hermetically sealed bunker.