There has been a dearth of vocal Republican moderates on the main stage of American politics of late. Enter Mike Castle of Delaware, a nine-term GOP congressman. Castle announced today that he's running for Vice President Joe Biden's old Senate seat. Castle's likely opponent is the vice president's son, state Attorney General Beau Biden.

Castle upends the Delaware Senate race. Top Congress wonk Stu Rothenberg immediately moved the race's ranking from “Currently Safe for Democrats” to “Lean Takeover for the GOP.” Speculative polls back Rothenberg's analysis. Castle has been elected statewide for a quarter century, including two terms as governor. He is now one of Republicans top prospects to crack into Democrats' Senate majority.

Castle's impact will not stop there. Castle is a throwback to a dying breed of Northeastern moderate Republicans. Republicans now have a moderate campaigning in one of the nation's premier 2010 Senate races. The Biden factor means outsized national media attention. Castle may bring the GOP some good press.

Today, Castle was careful to touch on “civility and bipartisanship.” He earned national attention this past summer at a town hall meeting. Castle was asked why Congress was not investigating claims that Obama was not born in the United States.

“If you're referring to the president, then he is a citizen of the United States," Castle replied. The crowd erupted in angry boos. Castle remained composed.

It was an image Republicans need more of. And Castle will likely offer it.