"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," Ryan said in a statement.
Democratic Sen. Herb Kohl announced Friday that he would not seek a fifth term. With local politics still roiled by Republican Gov. Scott Walker's controversial collective-bargaining changes, and Democrats' narrow majority in the Senate at stake, the race has the potential to emerge as one of the most fiercely contested of the 2012 congressional campaign.
Though Ryan is out, Republicans may soon have another heavyweight candidate.
Tommy Thompson, who was elected to an unprecedented four terms as Wisconsin's governor and was secretary of Health and Human Services under President George W. Bush, has told Republican Party officials that he would run if Ryan did not.
Thompson has long sought a return to elected office, even briefly running for president in 2008. The Wisconsin Democratic Party took a preemptive shot at his possible Senate candidacy.
"Thompson has been too busy taking lobbying cash from Big Oil and Wall Street to stand up to the divisive, anti-Wisconsin agenda of Paul Ryan and Scott Walker," state Democratic Party Chairman Mike Tate said in a statement.
No Democrats have come forward yet. Speculation centers on former Sen. Russell D. Feingold, who lost his seat in 2010. Reps. Tammy Baldwin and Ron Kind, along with former Rep. Steve Kagan, are also said to be considering the race.