Tommy Thompson is the next establishment Republican that conservative groups are looking to topple.

The former Wisconsin governor is in the fight of his political career as he attempts to win the GOP nomination for the state’s open Senate seat. Two lesser-known Republicans, former Rep. Mark Neumann and state Speaker Jeff Fitzgerald, are aiming to best him in the primary, and Neumann has fuel from the influential Club for Growth.

Similar scenarios have played out across the country since the tea party burst onto the political scene. Though Thompson is a once-bright political star in the state and the best-known candidate, a volatile electorate and a late primary could put him on the sidelines.

Democrats have cleared the field for Rep. Tammy Baldwin to be the party’s nominee, so the Republicans will clash in a primary that will not be held until August.

Thompson was elected to four terms as governor and served as secretary of Health and Human Services in President George W. Bush’s administration. Some conservatives have targeted him for deficits and increasing the size of Wisconsin’s state government and have used his failed run for the Republican presidential nomination in 2008 to gin up the same anti-
establishment sentiment that has cost other candidates their races.

The loudest and earliest anti-
Thompson group is the Club for Growth, which endorsed Neumann. Enraged over what members view as a fiscally troublesome record, the club has launched an all-out effort to try to block Thompson from getting the nomination. That includes an August television ad starring President Barack Obama, who lauded Thompson in a 2009 weekly address for backing an early version of the Democrats’ health care law. PolitiFact Wisconsin rated the ad “half-true” and Thompson now refers to the law as “Obamacare.” Wisconsin radio station WRN reported last month that Thompson thought “a good share of the law” would be upheld as constitutional, but he sounded GOP talking points: “I think, overall, Obamacare should be eliminated, and I think things should be done to replace it.”

Would the club back Thompson in a general election should he win the nod? No.

“We don’t support people based on party, we support people based on principles. If you don’t have principles to stand on, we won’t support you,” spokesman Barney Keller told Roll Call.

But Thompson’s campaign bashed the club as a Washington, D.C., group telling “lies” and said voters remember the former governor as having cut taxes and created school choice and welfare reform.

“Attacking Tommy Thompson is like attacking Wisconsin,” his spokesman Darrin Schmitz told Roll Call. “It will backfire.”

The campaign also points to state Republicans lining up behind Thompson’s bid, including Attorney General J.B. Van Hollen.

Neumann came to Congress during the Republican revolution of 1995 and served two terms. He left the House to challenge former Sen. Russ Feingold (D) in 1998 and narrowly lost. He lost a GOP gubernatorial primary last year.

Wisconsin Democratic Party spokesman Graeme Zielinski labeled Neumann “a perennial loser.” But the attempts helped him build up his name identification.

In addition to his Club for Growth backing, Neumann was endorsed last week by conservative GOP Sens. Rand Paul (Ky.) and Tom Coburn (Okla.).

One GOP strategist in the state suggested endorsements from Senators with high national profiles won’t matter, and it’s still to be determined whether Sen. Jim DeMint’s Senate Conservatives Fund, which caused some mischief during the 2010 primaries, will get involved in this race. National tea party groups could join the Club for Growth and spend heavily against Thompson if they decide to weigh in, but Thompson seems to have locked in strong local support.

“He’s got a lot of old-guard Republicans, people who are involved in politics, have been involved in politics, that are in government affairs or loyal backers in communities that are doing some grass-roots outreach on their own to build message and to support his candidacy,” said outgoing Jefferson County Republican Party Chairman Matt Banaszynski, who is unaligned in the race. “It appears that he’s got this pretty big presence.”

Neumann and Fitzgerald have ties to Gov. Scott Walker (R).

Neumann lost a gubernatorial primary to Walker after a fight operatives described as “pretty nasty.” Fitzgerald has worked closely with Walker as state Speaker.

Walker’s anti-collective bargaining efforts have rocketed him to the national stage as interest groups prepare for a Democratic-led recall effort next year.

The potential recall is consuming most of the political oxygen in the state. As Democrats and unions were preparing to launch the effort last week, Walker paid to air an ad during the Green Bay Packers’ Monday Night Football game. The ad featured a school board member praising the governor for giving the board “options” to manage the budget. “Wisconsin’s best days are yet to come,” Walker says in the ad.

If the anti-Walker movement obtains the required signatures necessary to move forward with a recall, it is estimated that election will take place in May or June, depending on legal maneuvering.

In addition to that activity and the Senate battle, Wisconsin will be a battleground in the presidential contest. So Badger State voters should expect to be inundated with political activity through Nov. 6.

Roll Call rates the Senate race a Tossup.