COLUMBUS, Ohio – Rick Santorum stole a key endorsement from chief rival Mitt Romney on Friday as polls in Ohio and elsewhere suggest the former Pennsylvania senator has seized the momentum in the rollercoaster Republican presidential contest.

Amid the shift, however, are signs of stress within a disorganized Santorum campaign and intensifying questions about whether he can sustain a rise that came and went once before. Romney’s mammoth political machine — coupled with new scrutiny — will give Santorum little margin for error.

He was all smiles at the Ohio State House on Friday afternoon as state Attorney General Mike DeWine formally shifted his allegiance from Romney to Santorum, a decision that comes just 18 days before Ohio and nine other states host critical Super Tuesday contests.

“I just am very, very grateful that he would step forward in this fashion and lead a spark here in the state of Ohio that I think is going to deliver us a great victory on Super Tuesday,” Santorum said.

But on what should have been an overwhelmingly positive day, Santorum could not escape a campaign misstep from the day before.

Foster Friess, the main donor behind Santorum’s “super PAC,” created a stir Thursday when he suggested on national television that aspirin used to be an acceptable method for contraception.

“The gals put it between their knees and it wasn’t that costly,” he said.

Friess apologized Friday in a blog post. But Santorum was repeatedly forced to dissociate himself from his surrogate’s comments, which he later described as “a bad joke.”

Whether it was a joke or not, the comments drew unwanted attention to his own positions on contraception and women’s issues. Santorum has said that states should be free to ban birth control pills and condoms.

Speaking to reporters after the DeWine announcement, Santorum said he and his wife, as Catholics, don’t practice birth control.

“To be attacked on that, which I have been, that somehow or another that just because I personally believe this, that somehow now I’m going to be the uber-czar that’s going to try to impose that on the rest of the country, it’s absurd,” he said. “It’s absurd on its face, and it’s absurd based on my record in the Congress.”

The contraception flap, according to Republican observers, is evidence of an undisciplined campaign that is already stumbling under the weight of intensifying scrutiny.

Polling suggests significant numbers of voters still don’t know Santorum well. And he may struggle to win over female voters in particular as they begin to pay more attention, according to Phil Musser, a GOP strategist who doesn’t work for either campaign.

“I think in the next couple days, we could start to see some serious erosion with respect to female support for Santorum in the Republican primary,” he said.

The Romney campaign countered on another front in a conference call at roughly the same time as Santorum’s DeWine announcement. It was the third consecutive day the campaign hosted such a conference call, although each featured Romney supporters from different states.

John Sununu, a former White House chief of staff and a Romney supporter based in New Hampshire, described Santorum as “a candidate who loves spending and frankly supports liberal labor causes and liberal social causes, like giving voting rights to felons.”

Actually, Santorum in the Senate supported restoring voting rights to felons once they had completed their sentence or parole.

He shrugged off DeWine’s defection, suggesting DeWine was upset by a Romney-friendly super PAC ad playing up the vote on felons. Romney and his allies have flooded the airwaves in Michigan, which, along with Arizona, holds presidential primaries Feb. 28.

Santorum’s allies expanded their television presence in Michigan on Friday as well, raising the stakes for the looming contest in Romney’s home state.

The pro-Santorum Red, White and Blue Fund political action committee disclosed to campaign regulators on Friday that it had purchased $668,500 in Michigan TV ad time. The group also spent about $135,000 on pro-Santorum mail sent to the state’s Republican voters.

Despite being outspent so far, Santorum leads various recent polls in Michigan and Ohio.

Asked about the apparent shift, Sununu noted that Romney holds a substantial delegate lead.

“This is a long slog,” he said. “It’s not going to be decided early.Michigan-based Republican operative Jeff Timmer is among those who doubt Santorum’s staying power.

“Santorum really hasn’t gone through much of a public vetting process outside of Iowa,” he said. “There will be a reality check. But I don’t expect that he will go away.”