A bit of Trivia.......
During the State of the Union speech.

The reason is that the President, Vice President, Speaker of the House, Supreme Court Judges, Heads of State, Treasury Secretary, Senators, Congressmen, and other key figures are all assembled in a single room. An attack or even a single gunman could kill or injure a great many high value US targets. It is televised and viewed around the world, a terrorist could gain great fame and recognition in being seen taking these targets.

US Security, FBI, and CIA have stated this is their most dreaded hour.