Are Tuesday's primaries in Wisconsin, Maryland and the District of Columbia do or die for Rick Santorum? Piers Morgan finds out from the candidate -- in a one-on-one interview -- at 9 p.m. ET Monday. You can follow Kevin Bohn on Twitter @KevinBohnCNN.
Washington (CNN) -- Ads, phone calls and mailers have bombarded voters in Wisconsin in the days leading up to Tuesday's vote -- the next major battleground in the Republican presidential race.
The Badger State primary has gained significance over the last week as both Mitt Romney's and Rick Santorum's campaigns have indicated it could dramatically alter the momentum and duration of the race.
Romney and his allies have outspent their rivals by a little less than a 4-1 margin on television ads in the state, according to figures provided by an unaligned Republican media consultant that tracks ad spending in the nomination race.
Romney leads polls in Wisconsin and is expected to win in the District of Columbia and Maryland, which also vote Tuesday.
There is a growing call for Santorum to drop out of the race and allow the party to coalesce around Romney, but Santorum used his rival's spending in Wisconsin to dispute the notion the race is over.
"On a North Dakota radio station the other day, (former New Hampshire) Gov. (John) Sununu, one of Romney's chief spokesmen, tried to spin this, 'Well, this race is over, this race is over.' Well, then why is he spending $4 million in Wisconsin if this race is over? If it's over and there's no chance, then why he is bothering even campaigning anymore, if it's over?" Santorum asked Sunday.
Romney's campaign and the super PAC backing his candidacy, Restore Our Future, will have spent about $3.028 million in television ads through Tuesday's voting, while Santorum and the super PAC supporting him, the Red, White and Blue Fund, will have put out about $810,310.
Romney's campaign is playing one ad that criticizes Santorum over voting for bills that include family planning funds while saying he personally opposed such programs and another that touts the former Massachusetts governor's fiscal conservative credentials.
Restore Our Future's ads also hit the former senator over the family planning issue and use a Santorum speech in which he says, "I don't care what the unemployment rate is going to be. It doesn't matter to me." The commercial also highlights Santorum's votes on the debt ceiling and congressional earmarks.
Santorum's campaign previously had fought back on attacks that used the unemployment sound bite, saying, "Rick was making the point that the Santorum campaign is not based solely on unemployment rates -- it's based on returning freedom and restoring this country's greatness -- and it's a mistake for anyone to try and reduce the idea of America to just the 'economy,' " Santorum communications director Hogan Gidley told CNN last week.
Restore Our Future has deployed its financial juggernaut in earlier caucuses and primaries not only on TV and radio ads but also robocalls and mailers to tout Romney's record and attack both Santorum and Newt Gingrich.
The Red, White and Blue Fund's ad attacks Romney for raising fees in Massachusetts by more $700 million as governor and hits him on the state's health care reform effort, saying it "served as the blueprint for 'Obamacare' and its $1.7 trillion price tag. We just can't trust Mitt Romney."
The super PAC also devoted resources to robocalls, spending more than $62,000 to reach Wisconsin voters, according to a filing with the Federal Election Commission.
Several voters told CNN on Sunday that all of these ads were a turnoff and would not sway their vote.
"I'm just sick of them. They've been going on for a long time, and they're very negative. And I'm just tired of them. I just turn it to another channel," said Diana Hollander of Sun Prairie.
Laura Zielski, a Republican from Waunakee, said she had received more than 12 calls in two days.
"It was just, like, all the time," she said. "I don't like them because I am Republican. I don't like them pitting one against the other. Even the Romney campaign, and I'm for Romney, but I don't like that he would be down on Santorum. I would like us to be united."
Zielski said she was planning to vote for Romney despite the negative ads.
Arlen Leholm, an independent from Madison, has also been inundated with phone calls that start during the day and run into the evening.
"Oh my God, yes. Most of them were Romney calls but some Santorum. But I don't pay much attention to that. I listened to the first few all the way through."
One robocall from the Romney campaign attacks his opponent, saying, "Rick Santorum repeatedly supported big labor bosses" as well as claiming the former senator from Pennsylvania "joined liberal Democrats against collective-bargaining legislation." The latter apparently was a reference to Santorum's 1996 vote against right-to-work legislation that would forbid people applying for a job to be forced to join a union. The call ends again trying to link Santorum to "big labor bosses."
Labor issues are a controversial topic in Wisconsin as Republican Gov. Scott Walker faces a recall election after supporting a bill effectively to end collective-bargaining for public employees.
Santorum has said calling him a friend of big labor is not true. He said he voted for some of the bills supported by unions because they were important to many of his Pennsylvania constituents, although he would not back the measures on a national scale.
The super PAC backing Romney also is calling voters in the state to attack Santorum for having voted to fund the "ultraliberal, pro-abortion Planned Parenthood." That attack refers to bills Santorum voted for that included money for family planning. Santorum has said that while he personally opposed those programs, he reluctantly voted for that legislation because of other things included in the bills.
The recorded call ends by saying a voter "deserves a leader who stands up for our principles, not a Washington insider."
Some of the harshest attacks come in the mailers.
Restore Our Future spent at least $118,000 on direct mail in the state, according to filings with the FEC. One sent out by the pro-Romney super PAC -- obtained by CNN -- shows pictures of Santorum and Hillary Clinton. It goes after Santorum, saying he "has been in Washington too long ... he voted with Hillary Clinton to allow felons to vote. Rick Santorum thinks letting felons vote is a good idea."
Legislation that Clinton, then a senator, advocated would have restored voting rights to felons after they completed all parole or pardon requirements.
Another mailer asks, "What do you believe is our best path forward?" Above a picture of Romney, it says, "The American way," and above a picture of Santorum are the words "or the Washington way?"
The ad lists contrasts between Romney and Santorum. Romney is called a "conservative businessman" who created thousands of jobs and also eliminated a $3 billion deficit in Massachusetts as governor, while Santorum is labeled a "Washington politician" who as senator supported increases to the federal debt ceiling and voted to "spend millions on wasteful pork projects."
At the bottom, the flier says: "The facts speak for themselves."
Gingrich's campaign isn't spending any money in the state on ads, but the super PAC supporting his candidacy is. It bought $129,000 worth of cable time and spent $46,802 for radio and e-mail advertising and $12,500 for Web ads, according to FEC filings.
CNN political producer Rachel Streitfeld contributed to this report.