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ABC News' Shushannah Walshe and Gregory Simmons Report:

KENTWOOD, Mich. - Rick Santorum defended his campaign's robo-calling in Michigan urging Democrats to crossover and vote for him in this state's open primary.

His campaign did it "to prove the point we can attract voters we need to win states like Michigan," he told reporters as he exited a diner here.

In a tight face-off with Mitt Romney in his rival's home state, Santorum said it doesn't matter to him that the Romney campaign has voiced its opposition to the robo-calls, blasting them as "shameful desperation" and "dirty politics."

"When 53 percent of the voters in New Hampshire are not Republican, that's OK and when he goes out and recruits folks who aren't Republican that's alright, who aren't going to be the decisive votes in the election," Santorum said, referring to Romney. In New Hampshire, both unregistered voters and Republicans can vote in the Republican primary. In Michigan, Democrats can cross over as well.

"But when I go out and have a message of growth and opportunity instead of running negative ads or running robo-calls with my voice from four years ago, that's not a dirty trick and I didn't complain about it, I don't complain. You know what, I'm a big guy."

In other early primary states, robo-calls ran using Santorum's endorsement of Romney four years ago, making it seem as though Santorum was supporting the former Massachusetts governor again this election. The calls were never directly linked to the Romney campaign, but Santorum called them "cheap shots" today while exiting the New Beginnings Café.

At his second stop of the day, he greeted patrons and tried to persuade an undecided voter to support him. "We are not going to go on any apology tours. We are going to stand up for the values that made this country great," Santorum told the voter.

The man asked if Karen Santorum would be "OK" in the White House. "She'll be great, she'll be the best," Santorum replied.

The voter responded, "We like that, especially in Grand Rapids."

Santorum thanked customers for coming out to meet him today while a crush of media and customers trailed him throughout around the diner. One man welcomed Santorum to "God's Country," while another told the candidate he was "praying" for him.

"Thank you for your conservative values, God Bless you," a woman told Santorum.

He shook her hand and thanked her before he took off to head to the airport and a rally in the Super Tuesday state of Ohio. This is the first day that Santorum has had Secret Service protection and although he was wearing his signature sweater vest, it was a far cry from when it was the candidate, an aide and an adviser's truck driving around Iowa.

At least four cars with two black SUVs containing the candidate, staff and Secret Service detail brought Santorum to his two stops in Michigan. It was clearly an important day for the campaign: The candidate who usually travels with one aide was joined by his press secretary, deputy campaign manager and two other aides.

In Grandville earlier today, Santorum briefly popped into the Rainbow Grille to greet voters and press the flesh, urging people to head to the polls. The crush was even more intense than in Kentwood and, despite similar situations in New Hampshire and Iowa, Santorum seemed surprised at the crowd that came to greet him. He stepped behind the counter to shake hands and was greeted with "I'm going to vote for you" and "You're going to win today."

* This story has been updated