WASHINGTON — Republican-turned-Democratic Sen. Arlen Specter gained a Judiciary subcommittee chairmanship but also a potential primary challenger Thursday, the latest twists in a turbulent episode of party switching.

The good news-bad news day for Specter didn't stop there.

Former Pennsylvania Gov. Tom Ridge announced he would not challenge Specter next year. Ridge, a moderate Republican and the first homeland security chief, had been running about even against Specter in a hypothetical general election race.

"My desire and intention is to help my party craft solutions that both sides of the aisle can embrace," said Ridge, whose decision eliminates one major challenge to Specter.

In the primary, however, Specter may face Democratic Rep. Joe Sestak, a former Navy vice admiral from the Philadelphia suburbs. In an interview with The Associated Press, Sestak said he's seriously considering taking on the 79-year-old Specter.

Since becoming a Democrat, Specter has been at odds with his new party, voting against the Democratic-backed budget, expressing opposition to a government option on health care overhaul and maintaining his opposition to a bill that would make it easier for unions to organize. Democrats also questioned his support for Republican Norm Coleman over Al Franken in the Minnesota Senate race.