By Nick Carey
RHINELANDER, Wisc. (Reuters) - Two months ago, Wisconsin's Republican Party establishment, conservative donors and grassroots Tea Party activists pulled together to help Scott Walker become the first U.S. governor to survive a recall election.
But just days before Tuesday's primary election, Republicans in the state are divided between four U.S. Senate candidates, including a wealthy businessman with strong Tea Party backing and a four-term former Wisconsin governor.
"With so many undecided voters, it appears people will make up their minds this weekend," said Mordecai Lee, a political science professor at University of Wisconsin Milwaukee. "This is anybody's race to win and anybody's race to lose."
The campaign for the Senate seat being vacated by four-term Democrat Herb Kohl poses a test for conservatives pumped up after key wins over "establishment" Republicans in Senate primaries this year -- in particular Indiana state Treasurer Richard Mourdock's defeat of six-term U.S. Senator Dick Lugar and attorney Ted Cruz's recent victory in a Texas U.S. Senate primary over Lieutenant Governor David Dewhurst.
In contrast to Indiana or Texas, there is no clear favorite in Wisconsin. Conservatives are split between banking and real estate executive Eric Hovde and former U.S. Representative Mark Neumann. Their main opponent is former governor and U.S. Health and Human Services Secretary Tommy Thompson, who many on the right deem insufficiently conservative.
If Thompson wins, some observers say it will be in part because Hovde and Neumann split the conservative vote.
Recent polls have either shown Thompson with a shrinking lead or indicate the race is a toss-up. Neumann generally comes in third, with state Assembly Speaker Jeff Fitzgerald a sometimes distant fourth.
Adding to the late scramble for votes will be Republican presidential candidate Mitt Romney's choice on Saturday of Wisconsin's conservative U.S. Representative Paul Ryan as his vice-presidential running mate, analysts said.
The Ryan pick will distract from the Senate campaign, "making it very difficult for the candidates to get their last-minute messages out," said Charles Franklin, a professor of law and policy at Marquette Law School in Milwaukee.
Diluting attention away from the race may also lower turnout, something that has generally favored more conservative candidates in the past, Franklin added.
NOVEMBER STILL SEEN A TOSS-UP
The winner of the Republican primary will face U.S. Representative Tammy Baldwin, a Democrat, in November in a race that is widely considered up for grabs.
Although Democratic President Barack Obama won Wisconsin by 13 points in 2008, statewide elections in this Rust Belt state -- which President George W. Bush lost by around 10,000 votes in 2004 and 5,000 in 2000 -- have historically been close.
Republicans must win a net three Senate seats to take control of the U.S. Senate if Romney wins the presidency and four seats for control if Obama is re-elected.
Tea Party activists promise to campaign for whoever wins on August 14, as above all they want a Republican Senate majority to enable a repeal of Obama's signature health reforms. The Tea Party movement advocates fiscal conservatism and smaller government.
"The main prize in this race is a Senate vote against Obamacare," said Bonnie Ketterhagen of We Vote Burlington, a Tea Party group, who personally favors Hovde. "Whoever wins will get my 300 percent support."
With all the candidates touting similar Tea Party-friendly platforms of spending cuts and tax cuts, Wisconsin's Republican Senate race comes down to personal differences.
Neumann, the former congressman, enjoys the support of the conservative business group Club for Growth, which has spent some $1.6 million backing him, and Tea Party Express, a national group associated with longtime Republican strategist Sal Russo.
But Neumann sought the governorship in 2010 and his bitter, unsuccessful primary battle against Scott Walker -- now a conservative hero for curbing public sector unions and surviving the June recall -- alienated many Tea Party activists.
Hovde has invested $5.1 million of his own money in his campaign, roughly double what either Neumann or Thompson have raised. He has been endorsed by FreedomWorks PAC, an arm of the conservative national nonprofit FreedomWorks led by former House Majority Leader Dick Armey which has been heavily involved in the Tea Party movement.
FreedomWorks PAC executive director Max Pappas said the group's endorsement was based on polling the 22,000 grassroots activists on its Wisconsin email list. Eric Hovde received more support than the other three candidates combined, he said.
TAINTED BY OBAMA?
Conservatives have hammered Thompson, claiming that he supported Obama's health reform before coming out against it.
Thompson, 70, who was first elected to public office in 1966, says those claims range from "misrepresentation to an outright lie" and argues he is a true, seasoned conservative.
"We want somebody who has the experience to handle this job on day one, there's no room for on-the-job training," he said.
Thompson also says he is the only candidate who can appeal to Democrats and independents to beat Baldwin in a state that has not voted for a Republican president since 1984 and where Obama has consistently led Romney in polls.
"Whoever wins will face a very competitive race against Tammy Baldwin," Franklin said. "There is no question that race remains a toss-up."
(Editing by Peter Bohan and Cynthia Osterman)