Had half an eye on this for a few months, but sounds as if it’s becoming more serious:

The Northeast’s dwindling cast of Senate Republicans has Democrats circling Arlen Specter’s seat in Pennsylvania, convinced the party is well-positioned to make a competitive race out of the 2010 election.

Leading the pack of prospects — at least in celebrity — is Chris Matthews, the MSNBC “Hardball” host and a former Capitol Hill Democratic staffer. The Philadelphia native has been toying with a run for months, and this week he sat down with state Democrats to discuss the prospect of taking on the five-term GOP senator.

Matthews is a former speechwriter for President Carter and was an aide to Tip O’Neill, so it ain’t like he’s any stranger to the game itself, rather than merely commenting on it.

This month’s Cook Political Report, a nonpartisan political newsletter that handicaps races, cast Specter as among the four most vulnerable senators of the 35 up for reelection in two years. “He is increasingly isolated from his party as a Republican in a Northeastern sea of blue,” said Hershey, Pa.-based pollster Michael Young.

I don’t know - most of Pennsylvania remains pretty red, but as we saw here in what was once one of the reddest counties - that’s changing.