COLUMBUS, Ohio (AP) ― Rick Santorum courted conservatives in the U.S. Midwest in his battle with Mitt Romney for the Republican presidential nomination as President Barack Obama’s campaign team shifted gears to consider the possibility his opponent in the November election will be the former Pennsylvania senator.

Campaign officials confirm Obama’s Chicago-based organization has begun combing through Santorum’s background looking for possible lines of attack. It also emailed Obama’s Pennsylvania supporters this past week asking for material that could be used against Santorum in upcoming speeches and ads.

“Circumstances have changed,” explained Obama’s deputy campaign manager, Stephanie Cutter, on Saturday.

Santorum has surged in recent opinion polls after capturing Republican caucuses in Minnesota and Colorado and a non-binding primary in Missouri on Feb. 7. Several polls have shown him ahead in Romney’s native state of Michigan, where primary voters cast ballots a week from Tuesday. He is also leading in polls in Ohio, where he declared the state “ground zero” for his campaign on March 6, or Super Tuesday, when 10 states hold nominating contests.

Santorum has positioned himself as the leading conservative in the race, while Romney, a former Massachusetts governor, has struggled to win over the party’s conservative base and has been attacked for his shifting positions on sensitive issues like abortion and health care reform.

Romney not only grew up in Michigan, he is the son of a former governor. The primaries in Michigan and Arizona on Feb. 28 mark the end of a lull in the state-by-state contests to choose delegates to the party’s national convention in late August in Tampa, Florida.

Though Santorum and Romney are close in the polls, Romney is considered the Republican front-runner nationwide, with more delegates from state-by-state voting that are necessary to claim the party’s nomination. The multimillionaire also has far more money and a much stronger campaign organization than Santorum.

The two other rivals for the Republican Party nomination are former speaker of the U.S. House of Representatives Newt Gingrich and the libertarian-leaning Texas Rep. Ron Paul.

Paul on Saturday said at a fiery campaign rally in Kansas City that the U.S. is “slipping into a fascist system where it’s a combination of government and big business and authoritarian rule and the suppression of the individual rights of each and every American citizen.”

Santorum campaigned Saturday for a second straight day In Ohio, where he is depending on support from the small government, anti-tax tea party movement and religious conservatives to deliver a victory on March 6.

More delegates will be awarded in Ohio than in any other state except Georgia in the opening months of the Republican campaign. Ohio and Georgia are two of the 10 contests scheduled for March 6, a benchmark for the primary campaign that often decides who can continue to the next level.

In Ohio, Santorum, who is known for his social conservative views, said Obama’s agenda is based on “some phony theology. Not a theology based on the Bible. A different theology.’’ He later suggested that the president practices a different kind of Christianity.

The Obama campaign said the comments represent “the latest low in a Republican primary campaign that has been fueled by distortions, ugliness, and searing pessimism and negativity.’’

Even as he criticized Obama, Santorum also went after one of Romney’s most promoted achievements _ his leadership at the 2002 Winter Olympics in Salt Lake City, saying his success was based on getting Congress to allocate “tens of millions of dollars to bail out the Salt Lake games.”

The Romney campaign does not dispute that federal funds helped save the games. But they noted that Santorum voted for those earmarks, among with funding for many special projects in his own state, when he was a senator representing Pennsylvania.

“Sometimes when you shoot from the hip, you end up shooting yourself in the foot,” Romney spokeswoman Andrea Saul said. “There is a pretty wide gulf between seeking money for post-9/11 security at the Olympics and seeking earmarks for polar bear exhibits at the Pittsburgh Zoo.”

Santorum used a later appearance before the Ohio Christian Alliance to go after Romney for using his financial advantage as “as a club to beat anyone who gets in his way.”

Santorum planned to head on Sunday to Georgia, where Gingrich, a former Georgia congressman, is hoping to mount another comeback on March 6.

At a campaign stop in Suwanee, Georgia, Gingrich blamed negative ads run by Romney and a group supporting him for depressing voter enthusiasm and turnout in the Republican presidential contest.

“We have a target, it’s called Barack Obama. The Romney people don’t seem to get that,” Gingrich said.

Questions about whether Santorum can sustain his rise in the polls come amid signs of stress within his campaign, mainly disorganization. Romney’s machine, coupled with new scrutiny for Santorum’s view of social issues as well as governmental policies, will give Santorum little margin for error.

As an example, one misstep by a Santorum supporter kept the former senator off message at times for two days.

Foster Friess, the main donor behind the super Political Action Committee supporting Santorum, created a stir Thursday when he related on MSNBC an old joke about how aspirin used to be a method for birth control. “Back in my days, they used Bayer aspirin for contraception,” Friess said with a grin. “The gals put it between their knees and it wasn’t that costly.’’

Friess apologized Friday in a blog post. But Santorum was repeatedly forced to distance himself from his supporter’s comments, which Santorum described as “a bad joke.” The comments drew unwanted attention to Santorum’s own musings about “the dangers of contraception’’ and other women’s issues.

“Santorum has been in the position of explaining on all of these issues. And when you’re explaining in politics, you’re losing,” said Phil Musser, a Republican strategist who doesn’t work for either campaign.

As the Republican candidates remain distracted by their nominating fight, Obama has seen his ratings in the polls steadily rising as the economy _ by far his biggest weakness in the campaign_ continues to show signs of a recovery. He also scored a victory this week over congressional Republicans by gaining approval of a bill to extend a payroll tax cut.

Until now, Obama’s strategists have mostly been focused on Romney as the candidate with the best organization and most staying power. The Chicago team’s emails and postings took sharp jabs at Romney’s wealth and venture capital background, and his opposition to Wall Street regulation and upper-income tax hikes.

However, with all the attention on Santorum now, Obama’s campaign, at least, is reconsidering.

“I mean, who’d have guessed?” Obama’s Pennsylvania campaign director, Bill Hyers, asked in an email to supporters. He said it’s up to Pennsylvania to make sure the rest of the country `sees Rick Santorum’s true colors.’’