(Jae C. Hong/AP Photo)

MILWAUKEE - Rick Santorum took on the unions today, calling them "bullies" as he pledged solidarity with Wisconsin Gov. Scott Walker in his fight to strip public employee unions of much of their bargaining power.

"Look, I come from southwestern Pennsylvania, I grew up in a steel town. I represented one of the most heavy labor districts in the entire country. It was a 71 percent Democratic district," Santorum said today at the Defending the American Dream Summit. "And I know what it's like, you know, to fight the bullies. And there is no tougher bullies than the public employee unions, and I just want to say to your governor, I am for you, I am behind you, and I'm going to do everything I can."

Santorum also reiterated his challenge to Mitt Romney, his rival for the Republican presidential nomination, to hold a one-on-one debate in key primary states, pointing to the debates held between Barack Obama and Hillary Clinton during 2008 when they were the final contenders for the Democratic nomination

"I've actually asked for debates with Governor Romney, one-on-one debates. This race has clearly gotten down to two candidates that can win the nomination and four years ago, when that happened with Barack Obama and Hilary Clinton, there was a series of one on one debates. I'd love to have a one-on-one debate," Santorum told reporters after a speech at the Defending the American Dream Summit. "I hope one of the networks here would sponsor a one-on-one debate here in Wisconsin or in Pennsylvania and New York, or whatever the states are that are coming up after Wisconsin. We should have a series of debates, maybe one in the Midwest, one in the East, one in the West.

"If Governor Romney says he's the candidate that is the eventual winner, at least have him make the case, because he isn't," Santorum said. "All he is doing is running negative ads and playing process questions to the media. He's not talking about anything important. He's just talking about the delegate math."

Santorum first said he would like to have a one-on-one debate with Romney earlier this month in an interview with Jonathan Karl on "This Week."

"I'd love to be able to get one-on-one with Governor Romney and expose the record that would be the weakest record we could possibly put up against Barack Obama," Santorum said. "We can't nominate such a weak candidate."

Campaigning in the state ahead of the April 3 primary here, Santorum called Wisconsin a "little hybrid of" Michigan, Ohio and Illinois, but wouldn't say whether Wisconsin is a "must-win" state for him, instead directing attention to Romney's win-loss record as he bears the marker of "inevitability."

"You know what I keep hearing these must-win states for me. How about must-win states for Romney?" Santorum said.

Ask if he believes Romney has bypassed him and is focusing his attention on the general election, Santorum argued the cash Romney's campaign has poured into the state indicates he's still concerned with the threat Santorum poses.

"For someone that says that it's inevitable, he's spent a lot of money on inevitability. We're going to win today, I'm confident of that, we'll win today in Louisiana," Santorum said. "With today, we're going to win 11 states, 11 states for a guy, who three months ago was sitting at 2 percent in the polls with according to the recent numbers we're being outspent 55 to 1. That tells you the weakness of Governor Romney and the strength of our message."

"The only reason governor Romney is winning this race right now is because he's just overwhelming with spending, not because he has a message, not because he has a vision not because he connects with voters its simply negative ads, beating the other side up in such high numbers that he's able to squeak out little victories across this country in states that frankly he should be cleaning, mopping the floor up, given the money he's spending and the establishment behind him, governors, senators, congressmen, everybody. And he's not sealing the deal - that tells you, that's got to tell Republican voters something's wrong here and we need someone that can stand up to this barrage and that's what I'm doing," continued Santorum.