The relationship between faith and politics varies by which political party a voter identifies with, according to a Pew Research Center survey released last month.

About two-thirds of Republicans said their president must have similar religious beliefs; only 40 percent of Democrats shared the sentiment. Most Americans saw the two Democratic front-runners - Hillary Clinton and Bernie Sanders - as less religious than their GOP rivals, and half of adults said they would be less likely to support an atheist candidate.

Donald Trump, who leads Republicans in most national polls, was seen as less religious than his counterparts, garnering just five percent of participants who considered him "very religious."

The separation of church and state is expressed in the First Amendment of the U.S. Constitution, yet most Americans believe the two must intertwine when it comes to the presidency. Candidates answer questions about their faith both on the campaign trail and during presidential debates. They pander to specific religious denominations, depending on which part of the country they're visiting.

Come Election Day, faith may decide who unseats President Obama.

Ted Cruz and the evangelical vote

Texas Sen. Ted Cruz won the Feb. 2 caucus over Trump in large part to some 33 percent of evangelicals who polled in his favor.

"Let me first of all say, to God be the glory," Cruz declared last Tuesday night after being declared winner of the Iowa caucus. "Tonight is a victory for the grassroots. Tonight is a victory for courageous conservatives across Iowa, and all across this great nation. Tonight the state of Iowa has spoken."

Cruz grew up attending evangelical schools. He identifies as a Zionist and repeatedly warns that religious liberties are under attacks. Instead of separating church and state, Cruz brings them together.

"From the dawn of this country, at every stage, America has enjoyed God's providential blessing," Cruz told a Liberty University crowd last March. "Over and over again, when we face impossible odds, the American people rose to the challenge."

Southern voters, like many in Iowa, tend to lean towards very conservative candidates. Cruz may not win Tuesday's New Hampshire primary - where he's only expected to win between 15 and 17 of the evangelical vote - but his performance in the upcoming South Carolina primary may determine whether Catholics and Protestants are truly on his side.

Donald Trump's grasp of the Bible

On Jan. 18, Trump spoke to a crowd of about 13,000 evangelicals at Jerry Falwell-led Liberty University. After vowing to protect Christianity from "political correctness," the Republican front-runner mispronounced a Scripture verse.

"Two Corinthians 3-17, that's the whole ball game ... Is that the one? Is that the one you like? I think that's the one you like."

Laughter ripped through the staunchly religious crowd, most who have read and re-read the Bible since childhood. Trump's handling of the situation, and his aversion to talking about religion, has many believing his relationship with God is superficial, or that he isn't as learned in Biblical teaching as he's led on.

Southern Baptists leader Russell Moore tweeted that Trump is "trading in the Gospel of Jesus for political power," and evangelical writer Matthew Lee Anderson likened him to a televangelist. Others cite Trump's vow to ban all Muslims as a sign that he's not devout.

Still, the Pew survey found 52 percent of white evangelical Protestants support Trump, second only to former neurosurgeon Ben Carson. Seventy-three percent of right-leaning registered voters though he was "very/somewhat religious."

Marco Rubio's experience with syncretism

Of all the presidential candidates, Rubio may have the widest grasp on the country's predominate religions.

A practicing Catholic, Rubio has explored Southern Baptist and Mormon faiths. He attends a Baptists church while in Florida and a Catholic one while working in Washington D.C. His views on creationism, same-sex marriage, and climate change helped the Cuban-American senator win over hardline conservatives, many who catapulted him to a third-place finish in Iowa.

Like Cruz, Rubio campaigns on protecting religious rights, and said as much in defending Kentucky clerk Kim Davis last summer.

"We should seek a balance between government's responsibility to abide by the laws of our republic and allowing people to stand by their religious convictions," Rubio said in a statement to The New York Times. "While the clerk's office has a governmental duty to carry out the law," he added, "there should be a way to protect the religious freedom and conscience rights of individuals working in the office."

Rubio is the only candidate who can consider himself syncretistic; part of Catholic, Baptist, and Mormon faiths. While that may draw some to his corner, others may see this as a flip-flop of his religious views because each religion, while similar, taps into a different voter base.

Rubio appealed to every affiliation during one the Iowa GOP debate, saying Judeo-Christian values are what make America special.

"Why are we some of the most generous people in the world? Why do American contribute millions of dollars to charity? It is not because of the tax write off," Rubio said. "It is because in this nation we are influenced by Judeo-Christian values that teach us to care for the less fortunate, to reach out to the needy, to love our neighbor."

Hillary Clinton, Bernie Sanders, and unaffiliated voters

Neither of the two Democratic presidential candidates spends much time talking about their faith. Sanders, who went to Hebrew school like many young Jewish Americans, has gone on record as saying he is "not actively involved with organized religions."

"To me, it means that all of us are connected, all of life is connected, and that we are all tied together," Sanders told The Washington Post. He added that he believes in God, just not in the traditional sense.

Clinton, a self-described Methodist, told a New Hampshire crowd last Wednesday that she keeps a group of faith advisors closer by and fights to separate political ambitions from personal values.

"I get a scripture lesson every morning from a minister that I have a really close personal relationship with," Clinton said. "And, you know, it just gets me grounded. He gets up really early to send it to me. So, you know, there it is in my in box at 5:00 a.m."

"I have friends who are rabbis who send me notes, give me readings that are going to be discussed in services. So I really appreciate all that incoming."

Only 40 percent of participants in the Pew survey though Sanders was at least "somewhat" religious; 48 percent though the same of Clinton.

Sanders and Clinton appeal to atheists and less religious voters because they identify with a growing number of Americans who don't side with a single faith. Proof of religion's decreasing influence can be seen in the survey where 32 percent of unaffiliated people said it was a good thing. Seven-in-ten of these individuals said religious conservatives have too much control over the Republican Party.

To some, a candidate not considering himself Catholic or Protestant for the sake of choosing a side is a sign of openness to millions of Americans who don't consider themselves with a single sect of Christianity.