There are only a few constitutional requirements for someone to be elected president — that they be 35 or over and a "natural-born" citizen of the United States, as well a resident in the country for at least 14 years — but there are a number of unwritten traditions that have historically shaped the office of the presidency.

One of these unofficial guidelines has to do with religion: Every president but John F. Kennedy, who is the nation's first and only Catholic president, has been Protestant.

President-elect Donald Trump will be no different. Trump grew up in a Presbyterian family, attending church regularly.

Still, among the Republican candidates from whom he wrested a nomination for president, Trump didn't seem to draw heavily on his faith in his campaign messages.

An Iowa pastor praying for Trump on his campaign trail Jae C. Hong/AP

Paula White, a close spiritual adviser to Trump who's known him for 14 years, told CNN in October that Trump has always been more private about his religious principles. Trump had spoken to White following leaked audio of the then-nominee bragging about grabbing women "by the pussy."

CNN religion editor Daniel Burke wrote that it was worth noting that, when apologizing for what he'd said, Trump didn't draw on religion at all; he didn't call what he'd done a "sin" or ask for God's forgiveness. White said this fact alone shouldn't have any bearing on how people assess Trump's spirituality.

"If he suddenly came out all religious, that would seem staged to me," White told CNN. "Donald has never been public about his faith, and when he has tried, it has been futile. It's not his language, but that doesn't mean it's not his heart."

"Futile" may be just the word. When the Christian Broadcast Network asked Trump "Who is God to you?" Trump ended up rambling on about his golf course and how he was able to make "great deals." He bookended his response, though, with affirmations about the goodness of God.

Trump said, "Well I say God is the ultimate. ... Nobody, no thing, no there's nothing like God."