Say what you want about Arlen Specter – and lots of people are saying lots of things about him these days – he’s never backed away from a fight.

He’s survived decades in the U.S. Senate, and overcome several tussles with cancer.

For some reason I don’t think a primary challenge is going to faze him.

You may remember Specter has been in the headlines recently for bailing on the Republican Party, crossing the aisle and joining the Democrats.

In doing so he did something some Republicans have been trying to do for years. There is a big portion of the GOP that never particularly cared for Specter. They considered him too middle of the road, someone who could not be counted on to vote their wishes.

This year the veteran senator pushed the buttons of the conservative wing of the party by providing the crucial vote that cleared the way for President Obama’s stimulus program. The thunder from the right was palpable.

Conservative former congressman Pat Toomey, who almost got the best of Specter a few years back, announced he would challenge him again. The polls said he likely was going to win. Even Specter’s own polling data had him losing.

So what was snarlin’ Arlen to do? Voila! Reinvent himself as a Democrat.

Obama welcomed him with open arms, as did Vice President Joe Biden, an old friend from the Senate, and Pennsylvania Gov. Ed Rendell. It seemed like they were preparing a coronation for Specter as the party’s Senate candidate.

Not so fast. No one bothered to tell our very own Congressman Joe Sestak.

The 7th District Democrat, the man who showed 20-year incumbent Curt Weldon the door, is not all that thrilled with the way party leaders have fallen all over themselves to anoint Specter as their guy. It represented an often thought – but rarely spoken – sentiment among many in the party.

Sestak has basically said he’s going to run against Specter in the primary; he merely wants to sit down with his family to talk things over.

For the most part Specter has not responded to the possible challenge from inside his new party.

Not any more. On Sunday, Specter made it clear he never expected nor was he promised a clear path to the nomination.

And he has a message for Sestak: Bring it on.

Now the volley goes back to Sestak. The next big thing will be his formal announcement.

This one could get real interesting.