Former Health and Human Services secretary Tommy Thompson is planning to run for the Senate seat being vacated by Wisconsin's Herb Kohl, Politico's Mike Allen and Edward-Isaac Dovere report. Thompson served two terms as Wisconsin's governor before going to work for the Bush administration and considered running last year against Russ Feingold, who lost.

Rep. Paul Ryan, author of the House GOP's controversial 2012 budget plan that would overhaul Medicare, is also weighing a run for Kohl's seat, and Thompson doesn't want to run against him. Ryan has said he'll decide whether to jump in the race or hold onto his powerful chairmanship of the House budget committee. Wisconsin Republicans told Politico's David Cantanese that Ryan was "only five months into his dream job... Why throw that away?"

Politico reports that if Thompson gets in the race, it will be "one of the most watched in the nation," thanks to the state's weeks-long protests over Gov. Scott Walker's push to curb public unions' collective bargaining power. Some have speculated that Feingold will enter the race for Kohl's seat, though his staff said campaigning next year "is not something Russ is eager to do or has been planning to do."

Update: Ryan says he won't run for Senate, National Journal's Major Garrett reports. As soon as Ryan announces his decision to stay in the House, Thompson will announce his candidacy.

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Elspeth Reeve