Former Pennsylvania Gov. Tom Ridge will not run for Senate, dashing Republicans’ hope of fielding their top candidate to run against Sen. Arlen Specter (Pa.) next year.

Republicans started recruiting Ridge last week, after Specter announced he was switching parties and would run as a Democrat in 2010 because he believed he could not beat conservative former Rep. Pat Toomey in the Republican primary. Ridge entertained the idea until Thursday, when the former Homeland Security secretary announced he would not run for Senate.

“After careful consideration and many conversations with friends and family and the leadership of my party, I have decided not to seek the Republican nomination for Senate,— Ridge said in a statement.

Ridge thanked his fellow Republicans for their encouragement but said he ultimately decided not to re-enter public life.

“The 2010 race has significant implications for my party, and that required thoughtful reflection,— Ridge said. “All of the above made my decision a difficult and deeply personal conclusion to reach.—

Several public polls showed Ridge well-positioned against Specter in a general election and also showed him crushing Toomey in the GOP primary. The same polls also showed Toomey is not likely to win a general election in Pennsylvania against Specter or another Democrat.

Specter, meanwhile, might have a primary of his own. Rep. Joe Sestak (D-Pa.) is considering challenging the former Republican, plus former National Constitution Center President Joe Torsella (D) is also still in the Senate race.