[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2009/images/02/11/art.getty.arlen.specter.jpg caption="Sen. Arlen Specter said he's staying a Republican."]
WASHINGTON (CNN) - Pennsylvania Sen. Arlen Specter says he's staying a Republican - but said an independent run is "always something that could be a possibility."
"I'm staying a Republican because I think I have a more important role to play there," he told The Hill earlier this week. "I think the United States very desperately needs a two-party system. … And I'm afraid that we're becoming a one-party system, with Republicans becoming just a regional party."
The moderate senator was one of three Republicans to vote for the stimulus bill - a move, he later said, that put him in some "political peril."
A likely primary re-match from Club for Growth president Pat Toomey - coupled with recent surveys that showed him receiving far higher marks from Democrats than from GOP voters - has sparked speculation the vulnerable incumbent might bolt the party.
"It's pretty hard to run without a party," Specter told The Hill. "It's always something that could be a possibility. But then I wouldn't be in the Republican caucus - wouldn't have quite the standing as a Republican."
He said that if he decided to run as an Independent, he would continue to caucus with Republicans, just like Sen. Joe Lieberman, an Independent, votes along with Democrats.
But Specter would have a harder decision than Lieberman, decided to run as an Independent after losing the Democratic primary in 2006. Pennsylvania election laws force candidates to declare their party affiliation before the primary.