When Rick Santorum accused President Obama of having “some phony theology” last weekend, it was neither an isolated event nor an offhand remark.

Instead, Santorum’s comments were a new twist on a steady theme of his Republican presidential candidacy: that Obama and other Democrats have a secular worldview not based on the Bible, one they are intent on imposing on believers.

Campaigning in Iowa in December, Santorum said Obama and his allies have “secular values that are antithetical to the basic principles of our country.” In Des Moines a few days later, he said the same people adhere to a “religion of self” rather than one based on the Bible. Speaking to a group of ministers in Plano, Tex., earlier this month, Santorum argued that the left is “taking faith and crushing it.”

In Tucson on Wednesday, Santorum said the president is “systematically trying to crush the traditional Judeo-Christian values of America.”

Santorum has regularly argued on the campaign trail that Obama and his allies’ views on abortion, same-sex marriage and the proper role of government prove they have distinctly secular values — and that the election offers a key and perhaps final chance for religious people to fend off their intrusions.

The relationship between religion and government has emerged as a flash point in the presidential campaign in recent days after an effort by the Obama administration to require religious institutions to include contraception in health insurance plans for employees. All of the Republican candidates objected to the effort, which the administration tweaked after a massive outcry, especially from Catholics.

But even in a nominating process heavy on Christian themes, Santorum, who is Catholic, stands out for his comfort in embracing religion. His contention that government is intruding into religious liberty predates the Obama decision.

After he made the “phony theology” remark, Santorum said he was discussing the president’s environmental policies, not questioning his Christian faith. And Hogan Gidley, a Santorum spokesman, said the media are more focused on such comments than voters are. Gidley said news stories have put too much emphasis on Santorum’s comments about religion and not enough on his views on job creation, improving manufacturing and slowing government growth. And, he said, they fail to properly cast them as part of Santorum’s “overarching theme” about the role of government.

“He discusses religion in a broader context, that we are given rights, we are endowed by our Creator with rights, and those rights are being taken away when government grows in size,” Gidley said. “People clap for that. They don’t gasp. People say, ‘Yes, our rights do come from God and yes, the government is taking them away.’ ”

During his December stop in Marshalltown, Iowa, Santorum made his case in typically emphatic terms. Opposition to abortion, he suggested, is the only logical conclusion of core American beliefs. He raised the promise, made in the Declaration of Independence, that all people are endowed by their Creator with certain inalienable rights.

“Do we still believe that?” Santorum asked. “If everyone is endowed by God — not any god, but the God of Abraham, Isaac and Jacob, that God, with the right to life, then there are certain things that we need to follow through and have in our law.”

Santorum does not limit his emphasis on religion to religious settings. Last week, in a speech ostensibly focused on the economy, he said Obama’s proposal to limit deductions for upper-income taxpayers, including for charitable donations, was a direct attempt to reduce the role of churches and other civic organizations in people’s lives.

“We need to create a rich society with lots of places for you to go before you go to the government for help and assistance in the problems that you’re dealing with. Charities, churches. It’s no wonder that the president, one of his tax proposals, sought to limit charitable contributions. They get in the way of government, you know, in providing for you,” Santorum told the Detroit Economic Club. “Families get in the way of government and your reliance on it.”

It was his comments about Obama — which he said were about the president’s environmentalism rather than his faith — that landed Santorum in the spotlight just as his candidacy was surging. He spent most of last weekend explaining his remarks.

In an interview on CBS’s “Face the Nation,” Santorum said he does not question whether Obama is a Christian. He insisted that his comment about Obama’s “phony theology” was being misconstrued.

“I accept the fact that the president is a Christian,” he said in the interview.

Two days later, Santorum blamed the media for picking the theology remark out of his “hundreds and hundreds of hours” of speeches and town halls, delivered without teleprompters. He said that voters find his unscripted speak-from-the-heart style refreshing and authentic.

“I’ll defend everything I’ll say — because it comes from here,” he said, indicating his heart.

At the same time, Mitt Romney has made similar claims about his Obama and religion in the wake of the contraception controversy, arguing at a town hall in Michigan on Tuesday that Obama associates with people with a “secular agenda” who have “fought against religion.”

Yet Santorum’s comments have the potential to sound extreme. Earlier this week, the Drudge Report led the day with a report of a 2008 Santorum speech in which he warned that Satan had set his sights on the nation.

That and other stories make some Republicans nervous about the prospect of a Santorum nomination, which independents could view as divisive and Democrats could use as a rallying cry.

“I think historically, religion has been divisive when it’s gotten connected with politics,” said John Danforth, who served 20 years as a Republican senator from Missouri. “I think Republicans are better if they stick with the big issues and the economic issues and the power of government and don’t frame it in religious terms.”

An ordained Episcopal minister, Danforth argued in a pair of 2005 New York Times columns that Republicans had become too entangled with the religious right. He has endorsed Romney but said he has not “fallen into a faint” over Santorum’s words.

“I don’t think that Santorum would say that people who don’t agree with him are not religious people,” Danforth said.

Republican pollster Whit Ayres said he does not think that Santorum has questioned Obama’s Christianity or the sincerity of the faith of his opponents. But he urged caution.

“It is very shaky ground to even come close to the line,” he said. “It tends to blow up in your face, politically.”

To some, Santorum’s language is part of his appeal, said Bob Vander Plaats, president of the Iowa-based Family Leader, whose endorsement helped Santorum defeat Romney in the state’s caucuses.

“He’s transparent, he’s authentic and he’s not trying to play games with his message,” Vander Plaats said. “I think it goes to the core of Rick Santorum. I’m quite sure he believes that this is a battle of worldviews and the worldviews are simply ‘God is’ or ‘God isn’t.’ ”

He said Santorum will attract independents looking for authenticity rather than a candidate who falls in the “mushy middle.”

Staff writer Felicia Sonmez in Arizona contributed to this report.