Rep. Joe Sestak (D-Pa.) left the door wide open to running against Sen. Arlen Specter (Pa.) in the Democratic primary next year during a cable news network interview Friday.

In an appearance on MSNBC’s “Hardball with Chris Matthews,— Sestak said he has not ruled out challenging Specter and said he is in the process of listening to Pennsylvania residents before deciding whether to enter the Democratic primary.

Specter switched his party affiliation and became a Democrat this week, acknowledging polls showed he could not win the GOP nomination in 2010. Since his switch, top party leaders — including President Barack Obama, Senate Majority Leader Harry Reid (Nev.) and Pennsylvania Gov. Ed Rendell — have publicly promised to support him as a Democrat.

In the interview, Sestak made it clear that he was not afraid to run against the party establishment — including Obama. He recalled that when he first decided to run for Congress in 2006, he didn’t know what the Democratic Congressional Campaign Committee was.

“Look, I don’t think politics is a sport and I don’t think President Obama, who I have such respect for, really can dictate what happens,— Sestak said.

Sestak has $3.3 million in the bank that he could put toward a Senate bid or use to run for re-election in the House. When pressed about a timeline for his decision, Sestak said it would be within this fundraising quarter or soon after.