PHILADELPHIA — Knock, knock. Who’s there? It’s former Sen. Arlen Specter and he’s continuing his second career as a comedian.

The longtime Pennsylvania senator performed at an open-mic night Tuesday at the Helium Comedy Club in Philadelphia, continuing a post-politics foray into standup comedy.

Specter told the crowd he’s “been in comedy now for 30 years” and took shots at former Pennsylvania Gov. Ed Rendell, New Jersey Gov. Chris Christie and others in his act.

The crowd roared with approval at Specter’s jokes.