The Secret Service has traditionally enlisted local law enforcement agencies for assistance everywhere they've gone. Until two weeks ago, their agents were there to supervise local resources, even to the point of checking that each and every applicable man-hole cover was welded down.
For the Trump assassination attempt, they barely even showed up at all.
However, they did SPECIFICALLY identify Thomas Crooks as a threat 10 minutes before Trump took the stage.
Ask me if it was a coincidence that they did absolutely NOTHING about that.