The federal Constitution is pretty clear on this matter. Quoting from Article VI, paragraph 3: "... no religious test shall ever be required as a qualification to any office or public trust under the United States."
That means the government cannot require candidates to hold a particular religious belief, or even be religious at all. However...
"Every significant presidential candidate from the major parties in American history has always espoused some form of religious faith."
That's Bob Stacey, the interim provost and an associate professor of government at Houston Baptist University. He says while there's no religious litmus test in the constitution, there certainly is one among voters. A survey this spring found that 61% percent of voters would be less likely to support a candidate who did not believe in God.
Carrol Doherty is with the Pew Research Center For The People And The Press.
"That's about the same as in the previous presidential campaign in 2008. And of the 14 traits or characteristics we asked about, that was by far the biggest negative."
Meaning a lack of belief in God hurt candidates more than a lack of political experience, or a past that included an extramarital affair.
But history shows that espousing faith doesn't tell us much about a particular candidate. Houston Baptist University's Bob Stacey uses the example of President Carter. Stacey says Mr. Carter made a big deal about being a born-again Christian, and attracted a lot of evangelical voters in 1976 — only to have those voters sour on him four years later.
"Jimmy Carter was really not what probably most born-again Christians were thinking of — in terms of his domestic policy. Some of his economic policies were very much of the more liberal tradition. I think he's widely perceived by evangelicals as soft on the Soviet Union, and they wanted a much harder line."
Stacey says other devout presidents have not always put religion at the core of their policy decisions.
"A good example from the George W. Bush administration was his compromise on stem cell research, which probably left neither side very well-satisfied. But his supporters thought they had their man, and they were probably more disappointed by his splitting the difference there."
Today, voters and pundits are focused on Mitt Romney's Mormon beliefs. But Stacey predicts the emphasis on any candidate's personal faith is due for a change. He believes in the coming years, voters, particularly conservative Christians, will spend more time considering a candidate's overall ideology than that person's specific denomination.
This article first aired 10-17-2011.