We knew this hard-hitting spot was coming, it was just a matter of when.

In a new TV ad, Rep. Joe Sestak (D-Pa.) is calling out Sen. Arlen Specter (D-Pa.) for the three decades that he spent as a Republican, and he’s doing it in the most effective way possible: using footage of former President George W. Bush proclaiming, “I can count on this man. See, that’s important. He’s a firm ally.”

Then the spot shows a smirking Specter, saying, “My change in party will enable me to be re-elected.”

Sestak is taking on Specter in the May 18 Democratic Senate primary. The Congressman’s campaign did not immediately responded to a request for information about how big the ad buy is or where the commercial is running. The Campaign Group produced the spot, which closes by saying, “Arlen Specter switched parties to save one job … His. Not Yours.”