LACROSSE, Wis. — Republican presidential front-runner Mitt Romney is attacking rival Rick Santorum as a friend of "big labor" as they campaign in Wisconsin, where a fight over labor unions is fueling a bitter recall effort aimed at Gov. Scott Walker.
Santorum, in turn, is aligning himself with the embattled Republican governor, a play for a party base that he hopes will carry him to victory in the GOP presidential primary on Tuesday.
"As you know the fight against big labor led by Gov. Walker isn't over, here in Wisconsin," a voice says in an automated Romney telephone call. "I was shocked to find out that Rick Santorum repeatedly supported big labor and joined with liberal Democrats in voting against right-to-work legislation during his time in Washington."
Romney, with help from a well-funded allied group, is pointing to union-friendly votes by the former Pennsylvania senator. His swing back from confronting President Barack Obama to attacking his main GOP rival comes as a Marquette University poll shows him overtaking Santorum in Wisconsin by an 8-point margin, 39-31.
In Michigan and Ohio, Romney criticized Santorum's 1996 Senate vote against so-called right-to-work legislation, which provides that people cannot be compelled to join a union as a condition of employment. The recession has hit hard in both states, and labor unions are unpopular with Republican primary voters there.
Wisconsin is Santorum's last chance to keep alive his claim that he can go toe-to-toe with Obama in the industrial heartland. Romney edged Santorum in Michigan and Ohio and soundly beat him in Illinois last week.
The pro-Romney super PAC Restore Our Future is spending $2.3 million on television ads attacking Santorum and added a spot this week mentioning his right-to-work vote.
Santorum has said as a candidate for president that he supports a national right-to-work bill, and that he opposed it in the Senate because he didn't want to undermine Pennsylvania's opposition to the policy. Santorum represented southwestern Pennsylvania in the House for two terms and then won two terms in the Senate from the strong union state. Romney supports national right-to-work legislation.
"Calling Rick Santorum a friend of labor is like calling Mitt Romney a conservative. Neither are true," Santorum told reporters Wednesday.
Organized labor and Democratic critics targeted Walker, a Republican elected in 2010, after he won approval last year in the GOP-controlled Legislature to effectively end collective bargaining for public employees. Campaigns for and against Walker have consumed months of television advertising and have overshadowed Tuesday's presidential primary.
Republican National Committee member Mary Buestin of Mequon, Wis., said GOP activists are lining up with Walker, and said any hint of waffling on union issues is not good for a presidential candidate.
"I think when people find out he voted that way, even if he has come around since then, it will hurt Santorum," said Buestin, who lives in a GOP-heavy Milwaukee suburb.
University of Wisconsin political science professor Charles Franklin, who conducted the Marquette poll, said GOP sentiment is heavily anti-union.
"The GOP primary electorate is very positive toward Scott Walker. So anything that differentiates a candidate and puts space between them and Walker is not good for the primary coming up," Franklin said.
Santorum worked vigorously this week to endear himself to supporters of Walker, who is locked in a tight battle to retain the governorship.
"Gov. Walker ... is leading. He is leading this country with his courage, his ability," Santorum said in Bellevue, Wis. "He is willing to stand up and fight the bullies. I come from southwest Pennsylvania. I represented the old steel valley of Pittsburgh. I know what it's like."
Outspent roughly 4-1 in the state by Romney and his allies, Santorum needs to rally Walker supporters to his side to have hope of prevailing in Wisconsin.
Aides to Romney noted how he campaigned for Walker ahead of the 2010 election, as well as Republican senators also targeted in the recall, including his state campaign chairwoman, state Sen. Alberta Darling.
Santorum has won a string of caucuses and primaries in the South and Midwest, where his socially conservative profile has appealed to evangelical conservatives more than Romney's more moderate, economic-focused message.
Santorum campaigned in conservative western Wisconsin on Wednesday and planned to return Friday.
Romney was planning to make his first campaign trip to Wisconsin on Friday. He talked for 30 minutes to thousands of Wisconsin voters in a telephone conference call Wednesday.
During the call Romney joked about an awkward familiarity with the state, where his father, as president of American Motors, moved all production. Later, when running for governor of Michigan, the elder Romney was walking in a parade where the marching band only knew the University of Wisconsin fight song.
"So every time they would start playing 'On, Wisconsin! On Wisconsin!' my dad's political people would jump up and down and try to get them to stop," Romney recalled with a chuckle.
The Democratic National Committee later accused Romney of joking about closing the Michigan motor plant.
Elliott reported from Wisconsin.