There might be a reason Pennsylvania Republicans so far have failed to find a challenger for Sen. Bob Casey. A new survey released this week showed the Democrat leading his real and potential opponents by at least 9 points.

A survey from Democratic firm Public Policy Polling showed former Sen. Rick Santorum as Casey’s strongest GOP challenger. Casey defeated Santorum handily in 2006, and the poll showed he would do it again in 2012, 48 percent to 39 percent.

The survey showed Casey leading two GOP Congressmen who expressed no interest in challenging him. He led Rep. Tim Murphy, 47 percent to 35 percent, and Rep. Jim Gerlach, 49 percent to 33 percent.

Casey also led his two lesser-known GOP challengers — attorney Marc Scaringi by 18 points and tea party organizer Laureen Cummings by 20 points. 

PPP took the opinion of 545 Pennsylvania voters on June 30, July 1-2 and July 5. The survey had a margin of error of 4.2 points.