Thompson said there has been a bit of renewed interest in the Senate race since last Tuesday’s gubernatorial recall election but noted activists are still feeling hung over from the highly emotional battle.

“You’ve got to realize that we never stopped campaigning in Wisconsin. You had the gubernatorial election in 2010, you had nine recalls in 2011 and the presidential primary in April in this year, and now you have this,” he said. “They’re so tired of campaigning, tired of giving, tired of volunteering, tired of making calls and going door to door handing out literature, and being called and seeing negative ads on television — they’re just tired out. You’re seeing less of a quick move to the Senate race, but you’re seeing slowly it’s picking up.”

Despite voter exhaustion, Thompson and his opponents are going strong — both he and Hovde started airing new ads in the last week, while Neumann stumped with Sen. Tom CoburnThomas (Tom) Allen CoburnMr. President, let markets help save Medicare Pension insolvency crisis only grows as Congress sits on its hands Paul Ryan should realize that federal earmarks are the currency of cronyism MORE (R-Okla.) over the weekend. And Rep. Tammy BaldwinTammy Suzanne BaldwinMcConnell: Midterms will be 'very challenging' for GOP Vukmir gets boost with Wisconsin Senate GOP primary endorsement  GOP senate candidate dismisses 'fake outrage' over remarks against Democratic veterans MORE, the likely Democratic nominee, began a statewide tour pushing for an extension of lower federal student loan rates on Tuesday.

The deep-pocketed, fiscally conservative Club for Growth has made it clear Thompson will be a top target, and has had a number of successes this year, most notably helping to defeat Sen. Dick Lugar (R-Ind.) and forcing Texas Lt. Gov. David Dewhurst (R) into a runoff.

Thompson said he was taking their threat seriously, and pointed to the 13 events he’d been to in the last week, including one in which he marched in a 2.5-mile parade in 90-degree heat.

And Thompson — who served four terms as governor, four years as a Cabinet secretary and a short time as a presidential candidate — repeatedly touted internal polling that showed 95 percent of Wisconsin voters know him and three-quarters hold a positive opinion of him.

“I think it’s going to be very difficult for any one of them to run a very credible campaign against me,” he said of his opponents. “I feel very good with the position I’m in. After not being on the ballot in 14 years, everyone still knows me as Tommy. Do you know any other politician, Democrat or Republican, whose name is out there and as soon as you say it people know who it is? I can go any place in the state, you say, ‘Tommy’ and they say, ‘Oh, the governor.’ And they don’t call me Governor, they don’t call me Mr. Secretary, everybody calls me Tommy.”

But while Thompson has held a lead in most polls, many observers expect that to tighten.

Thompson has already faced attacks about his stance on President Obama’s healthcare law. He backed early efforts for bipartisan healthcare reform legislation but opposed the later versions of the Democratic bill.

He said he’s long been opposed to the individual mandate, and noted, “As soon as they stopped being bipartisan and decided they were going to go with ObamaCare, I bailed.”

Thompson also defended his work as Health and Human Services secretary under former President George W. Bush, when he was instrumental in helping Bush push through a huge, unfunded expansion to Medicare. Thompson said if he had been in charge he would have found ways to pay for the bill.

“Much less was spent than what the [Office of Management and Budget] or the [Congressional Budget Office] ever estimated, and it is still doing a good job going in the right direction,” he said. “But you’ve got to realize that when you are a secretary and the president tells you, ‘This is the way,’ you do it. If I’d had my own way I would have figured out a way to pay for it, and that’s what I would do in the United States Senate.”

Thompson pointed out that Baldwin had long advocated for a government-run, single-payer healthcare system, and said the “huge divide” between them on that issue would be a defining one of the campaign if he wins the primary.

“Tammy’s so far left that [House Democratic Leader] Nancy Pelosi [Calif.] turns left to talk to her,” he said.