A year after quitting the GOP and becoming a Democrat, Sen. Arlen Specter is up against fierce competition from both parties for the seat he has held since 1981.
Last year, Specter was on the verge of being defeated in the Republican primary in his bid for a sixth term. Then, after voting in support of the Obama administration's stimulus package, he switched parties and became a Democrat.
If the 80-year-old Specter can survive a challenge in the Democratic primary, he'll face a formidable Republican opponent in November.
"If there is one political survivor in Pennsylvania, it's Arlen Specter," says Chris Borick, who teaches political science at Muhlenberg College in Allentown.
Borick says there are plenty of people who dislike Specter and relatively few who really like him. "But there are a large number of people in the commonwealth that begrudgingly respect Arlen Specter. And at the end of the day, it's been his secret to success," says Borick.
The question is whether that respect will continue now that Specter is a Democrat. After five terms in the Senate, Specter has alienated voters on the right and the left. Specter says his new party should reward his long-standing support for labor and abortion rights and his recent backing of the president's agenda.
"I supported Obama when the crunch came," Specter says. "When the stimulus package was up, it was my participation which was key, which led to enactment of the stimulus package. My voice was a strong one in support of President Obama's health care package."
Specter has the support of the White House and of party leaders. But not all Democrats are onboard. Former Navy admiral and current Pennsylvania Rep. Joe Sestak is challenging Specter in the May 18 primary.
"He deserted his party," Sestak says of Specter. "He left them in battle. And the independents don't trust him. The state of Pennsylvania needs a public servant -- someone who won't change their position or their party to keep their job."
Democrats hold a clear voter registration edge in Pennsylvania. But Borick says it's not clear how much that matters in 2010.
"There's a lot of fear on the Democrats' side that despite a trend where Pennsylvania has become more Democratic on paper, the actual ability of turning out people like they did in 2008 and 2006 is in question now," Borick says.
This year, it's Republicans in the state who seem to be more energized. The front-runner for the GOP nomination is former representative and former Club for Growth President Pat Toomey, who's running on a platform of lower taxes and smaller government.
"I think Democrats and independents are responding to my message of ending the bailouts, restoring fiscal discipline and bringing some balance to Washington. And I think that message is much more important than registration numbers," Toomey says.
Toomey came within 17,000 votes of beating Specter in the Republican primary six years ago. And several polls show Toomey leading the incumbent in a head-to-head matchup this time around. But Specter doesn't sound worried.
"I believe that when Toomey's record is exposed, that he has a 97 percent record with the American Conservative Union. Toomey's not far right; he's far out. And I think in a general election, we'll see," Specter says.
And if there's anyone who's made a career out of knowing what Pennsylvania voters are thinking, it's Arlen Specter.