New York City Mayor Michael Bloomberg was at a strip mall in north Philadelphia on Tuesday to help Rep. Joe Sestak (D-Pa.) appeal to independents in his run for Senate.

But the visit may have ended up helping Sestak only with his base. During his speech, Bloomberg said he backed, among other things, Sestak's push to close a loophole in gun-control laws, according to Fox 29. The remark wasn't included in a release the Sestak camp sent out with quotes from Bloomberg.

"I'm not a particularly partisan guy," the mayor told Fox 29 after the endorsement event. "I'm supporting people from both the major parties, Democrats and Republicans."

Bloomberg said he backs people who "look at the issues, rather than what the party leadership tell them."