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Newt Gingrich said the country is under attack by a the "secular left," Mitt Romney is concerned about President Obama's "secular agenda" and Rick Santorum has said repeatedly that the idea of an absolute separation of church and state makes him want to "throw up."

As the Republican presidential campaign drags on, the idea of a secular government is increasingly under fire. And Obama is personally under fire from Republican candidates, particularly Santorum,  who recently said the president's theology, especially where it comes to environmental laws, is " phony."

Obama's former press secretary said that comment "crossed the line."

But Americans by more than a 2-1 margin, 66 percent to 29 percent, say political leaders should not rely on their religious beliefs in making policy decisions," according to an ABC News-Washington Post poll from September of 2011.

This includes very narrow majorities of Republicans and conservatives, and much larger majorities of others.

Santorum apparently believes the most strongly about blurring the separation between church and state. He passionately defended his position in an interview with George Stephanopoulos Sunday, repeating that John F. Kennedy's famous 1960 speech pledging he would not bring his religion to the office of president "makes me throw up."

"To say that people of faith have no role in the public square?  You bet that makes you throw up.  What kind of country do we live that says only people of non-faith can come into the public square and make their case?" Santorum said.

He called the president someone "who is now trying to tell people of faith that you will do what the government says, we are going to impose our values on you, not that you can't come to the public square and argue against it, but now we're going to turn around and say we're going to impose our values from the government on people of faith, which of course is the next logical step when people of faith, at least according to John Kennedy, have no role in the public square."

Kennedy was the first and only Catholic president. He talked about his religion in 1960 in an address to protestant ministers.

"So it is apparently necessary for me to state once again not what kind of church I believe in - for that should be important only to me - but what kind of America I believe in. I believe in an America where the separation of church and state is absolute, where no Catholic prelate would tell the president (should he be Catholic) how to act, and no Protestant minister would tell his parishioners for whom to vote; where no church or church school is granted any public funds or political preference; and where no man is denied public office merely because his religion differs from the president who might appoint him or the people who might elect him. "

NPR has posted audio Kennedy's 1960 speech.

Fifty-two years later, Obama has come under attack for trying to tell churches what to do. The issue most at hand is a requirement by the Health and Human Services Department  that groups affiliated with churches - charities and hospitals, but not the churches themselves - must offer access to birth control in health insurance plans. The White House sought to soften the mandate by saying it is the insurance company that pays for the birth control coverage, but the criticism on the right that the administration declared a "war on religion" has persisted, particularly on the campaign trail.

Freedom of religion is a basic tenet of the United States. It states plainly in the First Amendment - the first changes the framers of the Constitution made to the document - "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof…".

That clause has been the subject of argument and interpretation ever since, whether it is prayer in schools or the 10 commandments displayed at a state capitol. Is it meant that religion should not be a part of government or that government must simply respect religion. If government is not free of religion - 80 percent of Americans call themselves Christian - would it essentially become a religious state?

Obama has showcased his own faith recently, suggesting at a recent prayer breakfast that an adherence to the teachings of Jesus might lead Republicans to support a tax increase for the wealthy.

One year earlier at the 2011 prayer breakfast, he spoke in depth about his own faith and his relationship with God.

But the president is much less popular among Americans who go to church at least once a week, according to a February poll by the Pew Forum on Religion and  Public Life. He wins handily among Americans who seldom or never go to church.

"I don't believe in an America where the separation of church and state is absolute," Santorum said Sunday. "The idea that the church can have no influence or no involvement in the operation of the state is absolutely antithetical to the objectives and vision of our country.

"This is the First Amendment.  The First Amendment says the free exercise of religion.  That means bringing everybody, people of faith and no faith, into the public square."

Santorum, a devout Catholic, is the most outspoken Republican on the issue, but his point has been echoed by two of his rivals.

Gingrich, who converted to Catholicism when he married his third wife, has also lashed out against what he perceives as a war on religion by "the secular left."

"The forces of the secular left believe passionately and deeply, and with frankly a religious fervor, in their world view and they will regard what I am saying as a horrifying assault on what they think is the truth," Gingrich said. "Because their version of the truth is to have a totally neutral government that has no meaning," said Gingrich in Georgia.

Mitt Romney, who is Mormon, has accused Obama of having a "secular agenda."

"You expect the president of the United States to be sensitive to that freedom and protect it and, unfortunately, perhaps because of the people the president hangs around with, and their agenda, their secular agenda, they have fought against religion," Romney said, responding to a question at a town hall recently about religious freedoms, in particular the Obama administration's recent controversial attempt to require all institutions, including hospitals and colleges with religious affiliations, to offer free birth control and other contraceptives.

Ron Paul wants a separated church and state, but he wants to return to a charitable system of churches and community groups to help the poor and the sick.

For Santorum, whose political brand is steeped in social conservatism, a desire to bring God into the oval office and policy is not unexpected. Although hearing him say a famous and much-cited John F. Kennedy speech makes him nauseous is jarring.

Santorum's view has not always been so clear cut. In 2006, during an ultimately unsuccessful bid for re-election as a senator from Pennsylvania, Santorum said he would support contraception and  public funding for contraception programs even though he was, as a devout Catholic, personally opposed to them, and thought contraception itself was "harmful to women."

Romney gave a speech in 2007 during his first run for the White House in which he sought to assuage a perceived concern among some Republican primary voters about his Mormonism.

"If I am fortunate to become your president, I will serve no one religion, no one group, no one cause and no one interest. A president must serve only the common cause of the people of the United States," Romney said in December off 2007 at the George H.W. Bush Library at Texas A&M University.

Obama's religion has long been the subject of speculation by conspiracy theorists and even some influential leaders who question it.

Rev. Franklin Graham, for instance, recently said he can't say for sure that Obama is a Christian, but he is sure that Rick Santorum is.