 That is calls for the head of the Secret Service to resign over security lapses in Pennsylvania continue. ABC News Chief Law and Justice Correspondent Pierre Thomas with more on the timeline of what happened. The morning of the event, congressional sources telling ABC News, the shooter came to the fairgrounds for an hour and later returned at 5 p.m., approximately one hour before he opened fire. Law enforcement sources tell us he was spotted walking near the magnetometers, did something suspicious, and was approached by authorities. He