The Wisconsin race has been going on largely under the radar, eclipsed for most of the spring by Gov. Scott Walker's recall election. But with that over, the Senate race is showing renewed signs of life as Thompson, a 70-year-old political giant, deals with three conservative Republicans trying to oust him in the Aug. 14 primary.
A Marquette University Law School poll released Wednesday shows that Thompson still has the upper hand, but one in four voters had yet to make up their minds.
"It's been so overshadowed by the recall election, voters haven't really formed opinions about a lot of things," said Marquette pollster Charles Franklin.
The poll showed Thompson with 34 percent support among likely voters, followed by former U.S. Rep. Mark Neumann at 16 percent, hedge fund manager Eric Hovde at 14 percent, and state Assembly Speaker Jeff Fitzgerald at 10 percent.
The random telephone poll of 344 likely primary voters was conducted June 13 through Saturday and has a margin of error plus or minus 5.4 percentage points.
The only Democrat running is U.S. Rep. Tammy Baldwin, a liberal from Madison who in 1998 became the first openly gay non-incumbent elected to a congressional seat.
Neumann has garnered the most support from tea party conservatives, including the Club for Growth which ran ads attacking Thompson in August months before he got into the race.
Club for Growth spokesman Barney Keller said Wednesday that voters still haven't focused on the Senate race because of the Walker recall, but as they do Thompson's support will wane.
"Right now Tommy Thompson's marginal lead in the polls is all due to name recognition," Keller said. "Republicans already suspect that Tommy Thompson isn't a true conservative, and once they realize it they'll look for a conservative alternative, and that will be Mark Neumann."
Thompson spokesman Darrin Schmitz said he suspected a flurry of attack ads targeting Thompson in the wake of the poll showing him with an 18-point lead.
The retirement of Herb Kohl opened the Wisconsin Senate seat that has been in Democratic hands since 1957. A victory in Wisconsin would be a major pickup for Republicans looking to regain control of the Senate. Republicans need a net gain for four seats to take control — or three if Republican Mitt Romney is elected president, which would give a GOP vice president the right to break ties in the chamber.
Tea party Republicans have been making a lot of noise across the country this year.
Last month, Richard Mourdock ousted 36-year Senate veteran Richard Lugar in Indiana, and state Sen. Deb Fischer used strong tea party support to upset two better-known and better-funded candidates in Nebraska. And Ted Cruz, a tea party-supported lawyer, emerged from a field of nine along with Texas Lt. Gov. David Dewhurst to send the Republican race to replace retiring Texas U.S. Sen. Kay Bailey Hutchison to a runoff.
Wisconsin is no stranger to the insurgent Republican movement. U.S. Sen. Ron Johnson came out of nowhere in 2010 to defeat incumbent Democratic Sen. Russ Feingold.
The tea party has had an impact on every Senate race in the country, forcing establishment Republicans to take more extreme positions, said Matt Canter, spokesman for the Senate Democratic campaign arm. That has allowed Democrats like Baldwin to focus on reaching out to voters, Canter said.
While Baldwin has yet to run a television ad, others have been busy attacking her.
The conservative group Americans for Prosperity Wisconsin launched a $400,000 statewide ad buy this week attacking Baldwin. That comes after the U.S. Chamber of Commerce, in conjunction with the state business group Wisconsin Manufacturers and Commerce, ran a Baldwin attack ad in February.
Neumann has been busy racking up support from tea party favorites including Oklahoma Sen. Tom Coburn, South Carolina Sen. Jim DeMint, and Kentucky Sen. Rand Paul. Neumann served in Congress from 1992 to 1996. He ran and lost for U.S. Senate in 1996 and lost in the Republican primary for governor in 2010 to Walker.
Hovde, a hedge fund investor who recently moved back to Wisconsin after spending 24 years in Washington, D.C., hopes to mirror Johnson's success. A political newcomer like Johnson was in 2010, Hovde was the first candidate running television ads, even during the Walker recall campaign. All of his ads so far have been positive, trying to boost his name recognition while he tries to carve out his niche as the outsider conservative candidate.
Hovde's had a few highly visible stumbles along the way. Most recently, Democrats caught him on video at a campaign stop last week at the Greater Brookfield Chamber of Commerce saying that the media should stop covering sad stories about low-income people who can't get benefits and instead focus on broader issues like the national debt.
"I just pray that you start writing about these issues. I just pray," Hovde said. "Stop always writing about, 'Oh, the person couldn't get, you know, their food stamps or this or that.' You know, I saw something the other day — it's like, another sob story, and I'm like, 'But what about what's happening to the country and the country as a whole?' That's going to devastate everybody."
Thompson launched his first statewide television ad of the campaign on June 7, two days after the Walker recall election. The ad doesn't mention any of his Republican opponents as he tries to stay above the fray — at least on TV. However, Thompson and Hovde have been trading shots at one another on the campaign trail in recent days.
The Marquette poll showed that Thompson was the only of the four Republican candidates ahead of Baldwin. He led her 49 percent to 41 percent. Baldwin and Neumann each had 44 percent, Baldwin led Fitzgerald 45 percent to 39 percent and she was ahead of Hovde 45 percent to 36 percent.
That question was of 594 likely voters with a 4.1 percentage point margin of error.