Sources have confirmed to RedState.com that Pennsylvania Senator Arlen Specter has decided to switch parties from Republican to Democrat..

Multiple House and Senate sources are telling RedState that Specter has concluded there is “no way he can win” a contested Republican primary in Pennsylvania, and that an announcement of his intent to switch from Republican to Democrat could come as early as today.

A “moderate” Republican, Specter has long been at odds with mainstream Republicans on spending and life issues, as well as several other positions. This February, Specter was one of only three Republicans in the U.S. Senate to vote in favor of President Obama’s (D) $787,000,000,000.00 “stimulus” spending bill. No House Republicans, and not all House Democrats, supported the “stimulus” legislation, and Specter, along with Maine Senators Olympia Snowe and Susan Collins, provided the GOP votes that enabled the measure to pass the Senate and be signed into law by Obama.

Specter is being challenged for his Senate seat by former Club for Growth president Pat Toomey. Sources say the decision to switch from Republican to Democrat was fueled in large part by a realization that he could not defeat Toomey in the 2010 Republican primary election.

Update: hogan has Specter’s statement.

Update 2: Just over a month ago, Specter told The Hill “I am staying a Republican because I think I have an important role — a more important role — to play there. I think the United States desparately needs a two party system. It is the basis of politics in America. I think each of the 41 Republican Senators, in a sense, and I don’t want to overstate this, is a national asset, because if one was gone you would only have 40. The Democrats would have 60 and they would control all of the mechanisms of government.”