From the pictures I saw, the USSS was blocked and being held. The only way for him to alert the President was to make the commotion. This did alert the President who came back. I do believe that this threw off the assassins. President Bush's quick response to the USSS agent most likely prevented his own assassantion
"This did alert the President who came back. I do believe that this threw off the assassins"
Words fail me.