In Wisconsin, Thompson turned back a trio of challengers to win the Republican Senate primary, setting up a general election race against Democratic Rep. Tammy Baldwin for retiring Democratic Sen. Herb Kohl's seat, which the GOP hasn't held since 1957.
Thompson's win, as an establishment Republican derided by rivals as not conservative enough, was a disappointment for tea party forces and other conservative activists hoping to add to big wins earlier this year in the Indiana and Texas GOP Senate primaries. Tea party candidates scored major gains in the 2010 congressional races, but they've had mixed success since then.
The win marked the first step in a political comeback for Thompson, 70, a former Cabinet secretary who hasn't been on the ballot since 1998.
He beat former U.S. Rep. Mark Neumann; businessman and political newcomer Eric Hovde, who spent at least $4 million on the race; and state Assembly Speaker Jeff Fitzgerald. Neumann had support from tea party forces as well as the anti-tax group Club for Growth.
Thompson's challengers cast themselves as closer to today's more conservative GOP than him.
Wisconsin Republicans hope they can build momentum from GOP Gov. Scott Walker's recall win in June and Republican presidential candidate Mitt Romney's decision to tap native son Rep. Paul Ryan as his running mate.