Corrected entry: The Secret Service massively under-reacts to Leary shooting at the president. Their policy is to keep their weapons off safety so that if they have to they can shoot quicker. They should have opened up on him with a hail of gunfire even if Horrigan was in the way. Watch the Reagan shooting and see how they normally react.
Rlvlk
29th Mar 2008
Correction: No one opened fire after Reagan was shot. They surrounded Reagan, threw him into the car and tackled Hinckley.
Rlvlk
The original mistake is correct. Reagan was immediately taken away and Hinkley was tackled by a number of policemen and agents. Evacuation happens in the movie but no-one goes after Booth, only 1 agent pulls his weapon and does not fire at the assassin! The outer ring of agents is completely missing so there is no-one to react.