AP

Republican presidential candidate, former Pennsylvania Sen. Rick Santorum waves as he leaves after speaking to supporters at Westminster Christian Academy Saturday, March 17, 2012, in Town and Country, Mo.

EFFINGHAM, Ill. -- Rick Santorum on Saturday guaranteed that a win in the Illinois primary will result in his nomination as the Republican presidential nominee.

"This is a primary, and turnout is everything. You do your job, you do your job, then this is the pledge," Santorum said. "If we're able to come out of Illinois with a huge or surprise win, I guarantee you, I guarantee you that we will win this nomination."

Illinois has largely been predicted to favor Mitt Romney for Tuesday's primary. The vote is expected to be driven by Chicago and its surrounding suburbs, pegged as unfavorable territory for the former Pennsylvania senator's brand of conservatism. But in areas like Effingham, hours south of the Windy City, Santorum hopes to fire up a Republican base that is often overshadowed by its Democratic counterparts to the north.

"You know you don't get a chance to out-vote your friends up in the Chicago-land area very often, but this is a primary and turnout is everything," he said, standing in a warehouse of a local business specializing in kitchen equipment.

While stumping in the Land of Lincoln, Santorum said he feels like he's already running in the general election.

“People ask me why I’m the best candidate to run against Barack Obama," said Santorum. "It’s because I feel like, in many respects, I am running against Barack Obama here in this primary because Mitt Romney has the same positions as Barack Obama in this primary.”

The health care bill that Romney signed as governor of Massachusetts is the issue Santorum has been hammering him on most frequently.

Santorum says the legislation laid the groundwork for the health care bill Obama signed in 2010, and therefore a Romney nomination would prohibit him from successfully running on a platform of repealing it.

Energy is another issue Santorum claims his Republican rival shares with Obama.  “Why, with sky rocketing gas prices, would we nominate someone who had the same position as President Obama with respect to fossil fuels?" he asked.

Santorum began his day stumping in neighboring Missouri, a state that held a non-binding primary that he won last month, but today is holding caucuses.  During a visit to a caucus site in Hazelwood, Santorum claimed dominance: "If you look at the Midwest, all of the Midwest is one color. It’s our color. We’ve won every state in the Midwest."

That statement dismisses Ohio and Michigan, two states Romney won, as part of the Midwest. Asked about it later in the day, Santorum said, "Well, I meant the heartland."

But even in the Show Me State, it was clear how important the primary happening happening across the Mississippi River will be to the Santorum campaign.  “When you leave here, go home, sign up on our website, start calling folks in Illinois. Because we’ve got a big election coming up in a couple days in Illinois," he pleaded. "Please help us out there. If you’ve got friends over there, make sure they get out and help us out."

And even with an aggressive campaign schedule in two states today, the Italian American still found time to show his St. Patrick's Day spirit.  On the stump he wore a green boutineer and his campaign manager tweeted out a picture of him enjoying a Guinness at an Irish pub between stops.

"I usually get there in the morning so I felt a little bad I didn’t get there until lunch time," he said of his March 17 traditional pilgrimage to the pub.

Update: In response to Santorum's comments on Saturday, Romney campaign spokesperson Ryan Williams had this to say:

"Senator Santorum is an economic lightweight who has precisely zero job creating experience. He ought to scare every conservative when it comes to his economic record. We won't get the economy going again by replacing one senator with no job creating experience with another with no job creating experience."