“There are material risks in the position I’m taking, which may well impact the  primary,” said Senator Specter. “Those thoughts have not escaped my attention.”
Still, he added, “I believe that my duty is to follow my conscience and vote where my faith is in the best interests of the country.”
Role of past GOP moderates
In the Bush years, GOP moderates, also including Sen. George Voinovich (R) of Ohio and former Sen. Lincoln Chafee (R) of Rhode Island, often acted as brakes: In 2003, their votes forced President Bush to trim a proposed $725 billion tax cut to $350 billion. They also consistently blocked legislation to permanently extend those cuts, on the grounds of fiscal discipline.
But for the Obama administration, they’re more likely to be the go-to facilitators on issues ranging from tax and entitlement reform to economic revival and regulation.
“Under certain circumstances, centrist votes are pivotal,” says John Pitney, a political scientist at Claremont McKenna College in Claremont, Calif. “This is one of those rare occasions where the margin is close and the stakes are high.”