(CNN) - Rep. Paul Ryan said Tuesday he won't run for the open Senate seat in Wisconsin, saying his efforts are best directed to tackling the country's fiscal issues in his post as chairman of the House Budget Committee.
“For my family and me, the most important factor in making this decision was determining where I could make the biggest difference," Ryan said in a statement. "Our nation is quickly approaching a debt crisis that will do serious damage to Wisconsinites and all Americans if it is not properly addressed. I believe continuing to serve as Chairman of the House Budget Committee allows me to have a greater impact in averting this debt-fueled economic crisis than if I were to run for the United States Senate."
That should open the door for former Wisconsin Gov. Tommy Thompson. Two separate GOP sources confirm to CNN that Thompson is expected to make a bid for the seat now held by Democratic Sen. Herb Kohl. The sources say Thompson told GOP officials he intended to run if Ryan decided against a campaign for the Senate.
Thompson also served as Health and Human Services Secretary under President George W. Bush and ran unsuccessfully for the Republican presidential nomination in 2008.
Kohl announced Friday that he will retire after serving four terms in the Senate. Kohl became the sixth senator in the Democrat's coalition in the chamber to announce their retirement in 2012 rather than run for re-election. Two Republican senators have also announced they won't run for re-election next year.
Democrats currently hold a 53-47 advantage in the Senate, but are defending 23 (21 Democrats and two independents who caucus with the party)
seats next year, compare to just 10 GOP seats up for grabs.'
During the 2010 midterm elections Republicans won two Democratic-held seats in Wisconsin as well as the governorship. Then-incumbent Sen. Russ Feingold was also unseated after serving three terms in the Senate.
Ryan Sunday told CNN's Candy Crowley on State of the Union that he would make an announcement this week on his political intentions.
The expected bid by Thompson was first reported by Politico. Other possible Republican candidates include state Senate Majority Leader Scott Fitzgerald, former Rep. Mark Neumann, former Rep. Mark Green, Attorney General J.B. Van Hollen and businessman Tim Michels.
Democratic Representatives Tammy Baldwin and Ron Kind are considering bids for the Senate seat.
The Democratic Senatorial Campaign Committee quickly reacted to word that Thompson may be jumping into the race.
"Tommy G. Thompson has spent the last decade doing the bidding of the Bush Administration and his special interest clients at his lobbying firm," said DSCC communications director Matt Canter, in a statement.
"The fact is that Tommy's Republican Party has changed dramatically in the decade he has been making money in Washington DC. Now his fellow Republicans want to end Medicare, take away the rights of working people and eliminate prescription drug coverage for seniors. Is Tommy ready for a makeover?" added Cantor.
The rival National Republican Senatorial Committee, which says it stays neutral in all party primaries for Senate, responded as well.
"Given that they were already facing a difficult political landscape and just saw another once-safe seat move into the toss-up column, it's not hard to see why national Democrats are engaging in desperate attacks," said NRSC Communications Director Brian Walsh. Perhaps they should focus less on the partisan rhetoric, and more on stopping any additional Democratic retirements."