Updated: 1:01 p.m.Rep. Mike Castle (R), a fixture of Delaware politics and a prominent centrist in the House, announced Tuesday that he is running for the Senate seat formerly held by Vice President Joseph Biden — a victory for Republican strategists in a Democratic-leaning state where Castle has been politically dominant.At a press conference in Wilmington, his hometown and the largest city in the state where he has held an at-large district since 1993, Castle said that “we need the strongest and the most experienced leadership we can find in this country today.—“I hope to be able to bring that to the United States Senate,— Castle said.Castle, a former Delaware governor, will become the early frontrunner for the seat currently held by Sen. Ted Kaufman (D), who was appointed earlier this year to succeed Biden. Kaufman is not running to serve the remaining four years of the term that Biden won in November 2008, simultaneous to his election as vice president.Republican strategists expressed confidence that Castle would help the GOP expand its 40-seat minority and also end its five-election losing streak in Delaware Senate races. A Republican last won a Senate race in the state in 1994, when the late Sen. Bill Roth was elected to his fifth term.“If he does [run for Senate], it’s game, set and match,— former Virginia Rep. Tom Davis, a former chairman of the National Republican Congressional Committee, said of Castle.“On the national scale, clearly the Republicans need to add to their Senate numbers, and I think he’s the guy to get it done here in Delaware,— Delaware state Rep. Greg Lavelle (R) said. “It doesn’t take a genius to figure out that [Minority Leader] Mitch McConnell and others would feel the same way, that the Congressman would run a great race in Delaware.—National Republican Senatorial Committee Chairman John Cornyn (Texas) said in a statement that his organization “will ensure that Mike Castle has all the necessary resources to win this seat next November.—But Democratic officials signaled that they would tie Castle to the positions of former President George W. Bush and the national Republican Party, which still has a poor image nationwide.“He built-up a record of supporting … George Bush’s economic policies, including tax cuts for the super-wealthy, that drove Delaware’s economy into a ditch — and now won’t support any of the Obama-Biden plans to fix it,— Eric Schultz, a spokesman for the Democratic Senatorial Campaign Committee, said in a statement. “This will be a race about who is positioned to lead Delaware into the future, and Democrats fully intend to hold onto the Vice-President’s seat.—John D. Daniello, the chairman of the Delaware Democratic Party, said he has “a lot of respect for Mike Castle,— but he “has been growing increasingly out of touch with Delaware voters.—The top potential Democratic candidate is state Attorney General Beau Biden, the vice president’s eldest son who just returned from a military obligation in Iraq as a captain in the Delaware Army National Guard. Beau Biden was elected to his office in 2006 and is up for re-election next year.A Rasmussen Reports poll conducted Sept. 30 suggests that a Castle-Biden race would be competitive: Castle had 47 percent and Biden had 42 percent.“I don’t have any illusions that this will be easy street. I realize this will be a very difficult election, and I’m sure the other side will be thinking the same thing,— Castle said.Castle had $861,000 in his House campaign account at the end of June, all of which can be transferred for use in a Senate race.Castle never faced threatening Democratic opposition in his re-election campaigns. He topped 65 percent of the vote in each of his first six races, and even his more modest showings in the past two election cycles — 57 percent in 2006 and 61 percent in 2008 — were impressive, given the strong Democratic trend nationwide and in Delaware those years.Castle, 70, already had all but officially ruled out seeking re-election to the House in 2010, and Democrats have a good chance at winning Castle’s seat now that the Congressman has eschewed a re-election bid. The likely Democratic nominee, former Lt. Gov. John Carney, began campaigning for Castle’s seat in April and raised $262,000 through the end of June.Potential Republican candidates for Castle’s seat include state Rep. Tom Kovach, who is a self-described “Mike Castle Republican—; Anthony Wedo, an investment and restaurant executive; former state Sen. Charlie Copeland, who was the party’s 2008 nominee for lieutenant governor; and Lavelle.