"Think if this guy ran for president today and someone googled him," said Sean Faircloth, executive director of the Secular Coalition of America, which advocates for a strict separation of church and state and encourages acceptance of nontheists.
Three Presidents, Jefferson, Abraham Lincoln and Andrew Johnson, were not affiliated with a sect of Christianity. But Lincoln often quoted the Bible and referred to God.
There have been some notable runs for the presidency by non-Christians: Connecticut Sen. Joe Lieberman, who is devoutly Jewish, was 537 votes in Florida in 2000 from being the first non-Christian vice president. But he failed miserably when he ran for president himself.
Mormon Mitt Romney, the Republican former Governor of Massachusetts, who failed to get the Republican nomination in 2008, will test the Protestant lock on the presidency if he runs again for president in 2012.
There is growing religious diversity in Congress, where the 2006 election saw the first-ever elections of both a Muslim, Rep. Keith Ellison of Minnesota, and two Buddhists in Reps. Hank Johnson, D-Ga., and Mazie Hirono, D-Hawaii.
In 2008, a second Muslim, Andre Carson, D-Ind., was also elected.
The proportion of Muslims in Congress -- 0.4 percent -- roughly mirrors their imprint on the larger population, 0.6 percent, according to a Pew study of faith in Congress.
Ellison caused a stir in 2007 when he was sworn into office on a Quran instead of a Bible.
The Pew study shows a similar correlation among Protestants, broadly, who make up about 51 percent of the population and 54 percent of Congress. Catholics are better represented in Congress, 30 percent, than they are in the population, 24 percent. Six percent of federal lawmakers are Jewish to their 1.7 percent imprint on the population. Mormon's are 2.6 percent of lawmakers, to their 1.7 percent of the population.
The most underrepresented faith group in the Pew study is unaffiliated, which claims no lawmakers, but 16 percent of the population. Five lawmakers don't specify their religion and one of those is Rep. Pete Stark, D-Calif., who is an admitted atheist, "a Unitarian who doesn't believe in a supreme being."
Faircloth of the Secular Coalition of America said, "The ultimate victory for all Americans would be that we simply don't talk about it."
Focus on the Family's Minnery said that kind of wholesale divorce between religion and politics cannot happen in the United States because politicians are more than happy, in many cases, to advertise their religion to voters.
"I say given the makeup of the people, politicians find it to their advantage to stress their connection to their faith," he said.
A study by Trinity College showed that 15 percent of Americans have no religion, but the number is far higher, 22 percent, among people 18-29. Having no religion is the fastest growing religious group in the United States, according to the Trinity study.
Minnery rejects the idea that there is a Christian litmus test in American politics.