Washington (CNN) - Sen. Arlen Specter, D-Pennsylvania, the only Senate Democrat to oppose Elena Kagan in the past, told CNN Tuesday he will not be pushed into declaring how he will vote on her Supreme Court nomination before Democratic primary voters decide next week whether to re-elect him.
"People would expect me to make a judgment after the hearing has been held, after we know what her views are and when the process has taken its course, people will not expect me to make a knee jerk reaction before I know the facts and the issues," Specter told CNN.
Specter voted against Kagan's nomination for Solicitor General last year. Back then, he was a Republican. Now he's in a neck and neck fight to keep his seat by winning the Democratic nomination in Pennsylvania's May 18 primary. Some polls show him now trailing his opponent, Rep. Joe Sestak, D-Pennsylvania.
Sestak is seizing on Specter's vote against Kagan for Solicitor General and accusing him of political opportunism and "backtracking" now.
Sestak is also banking on the fact that most Democratic primary voters would want their Democratic Senator to back President Obama's Supreme Court nominee, and is suggesting after next week's primary, Democratic voters won't be able to hold him accountable.
"The people of Pennsylvania have no way of knowing where he [Specter] will stand after May 18th," said Sestak in a statement Monday.
But in an interview in Specter's Capitol Hill office, he dismissed that.
"Well the voters expect me to do a job under the Constitution which requires going through the questioning and evaluating her performance. Congressman Sestak may be prepared to tell how he is going to vote before he knows what the issues are and what the facts are but I don't," said Specter.
In voting against Kagan for Solicitor General last year, Specter said he was frustrated that she would not answer his repeated attempts to find out where she stood on various issues.
He said he knows it will be even harder to get answers now.
"When you are up for Supreme Court Justice the tradition is that you don't ask a nominee how they would decide a specific case because of judicial independence," said Specter, "I have an open mind, I have been in a lot of confirmation proceedings, and I'm looking forward to it."
Specter's campaign released a new television ad in Pennsylvania Tuesday featuring President Obama's strong endorsement.
During the brief interview with CNN, Specter alluded to President Obama's support several times, and said that the President wouldn't expect him to announce his position on Kagan's nomination at this point.
"When President Obama first endorsed me months ago, he said he did not expect an automatic vote from Arlen Specter, he knows better than that," said Specter.
"My whole record is one of independence. He wants me to perform my constitutional duty, separation of powers, to evaluate the nominee in a thoughtful way. He trusts my judgment and I think the people of Pennsylvania do too," said Specter.
Specter switched parties last year when it became clear to him he could not win a Republican primary. He argued he could still help Pennsylvanians with his experience and seniority, and that becoming a Democrat was his best shot at succeeding.
But that pro-incumbent argument has lost its punch in such an anti-incumbent election year.
When asked if he made a political miscalculation about the atmosphere, Specter said he believes its only an anti-incumbent year "because people are dissatisfied with all the bickering and partisanship."
"My entire career in the Senate has been one of bipartisanship. I have crossed the aisle consistently," said Specter.
And what about primary voters who tend to demand purity over bipartisanship?
"I believe the primary voters want a thoughtful Senator who will make a considered judgment after knowing all the facts," said Specter, "and they don't expect me to come down with a decision on a Supreme Court nominee until there have been hearings and an opportunity to reflect on it and make that kind of considered judgment."