Republican leaders issued a unified message Tuesday as news reverberated on Capitol Hill that Sen. Arlen Specter (Pa.) is joining the Democratic Party: Good riddance.

National Republican Senatorial Committee Chairman John Cornyn (Texas) blasted Specter in wake of what he called his decision to switch parties “in the face of a seemingly insurmountable bid for re-election.—

“Senator Specter’s decision today represents the height of political self-preservation,— Cornyn said in a statement. “While this presents a short-term disappointment, voters next year will have a clear choice to cast their ballots for a potentially unbridled Democrat super-majority versus the system of checks-and-balances that Americans deserve.—

Just two weeks ago, Cornyn penned a letter to Pennsylvania Republicans asking them to support Specter’s re-election, calling him the GOP’s “best bet— to keep the seat in 2010.

If Specter had run for re-election as a Republican in 2010, he would have faced a primary rematch against conservative former Rep. Pat Toomey, who came within 2 points of defeating him in their 2004 race. Recent public polls showed Specter trailing Toomey by double digits in the primary, but the Senator performed well in the general election because of support from Democrats.

Republican National Committee Chairman Michael Steele also released a statement expressing his displeasure with Specter’s decision and vowed to defeat him in 2010.

“Let’s be honest — Senator Specter didn’t leave the GOP based on principles of any kind,— Steele said. “He left to further his personal political interests because he knew that he was going to lose a Republican primary due to his left-wing voting record.—

On Capitol Hill, House Republicans do not appear to be shedding tears over Specter’s departure from the party.

“After years of voting like a Democrat and putting political expediency before principle, it shouldn’t come as a surprise that Arlen Specter is joining [Speaker] Nancy Pelosi and [Senate Majority Leader] Harry Reid’s ranks,— said one House Republican aide with Pennsylvania ties.

Keystone State Democrats, meanwhile, wasted little time welcoming Specter into their ranks. Freshman Rep. Kathy Dahlkemper (D-Pa.) said in a statement that she looked forward to working on the same team as Specter.

“I look forward to continue working closely with Senator Specter to tackle the critical issues we face together, such as getting our economy back on track by creating good paying jobs,— Dahlkemper said.