So important is faith to voters in Iowa, every Republican candidate makes mention of theirs at every campaign stop they make across the state. Even a certain twice-divorced, thrice-married business tycoon has been at it. Half of Iowan Republicans call themselves evangelical or born-again Christians.
Democrats too have had to pay heed to those for whom God comes before president this year. So it was that Hillary Clinton found herself explaining how her version of worship has shaped her understanding of public service. It is not an area of her personal life she has often publicly shared.
The key, she said, was to see faith as something to foster empathy, not as a cudgel to “condemn so quickly” and “judge so harshly”.
“I am a person of faith. I am a Christian. I am Methodist,” she said at a local school gymnasium in Knoxville, Iowa, recently. “My study of the Bible and my many conversations with people of faith have led me to believe that the most important commandment is to love the Lord with all your might, and to love your neighbour as yourself. That is what I think we are commanded by Christ to do.”
Having been raised as a Jew in Brooklyn, the topic is trickier for Bernie Sanders. He too had rarely talked about faith until Iowa. His answer now is this: he believes in a God, but has drifted away from organised religion. “I think everyone believes in God in their own ways,” he recently told the Washington Post. “To me, it means that all of us are connected, all of life is connected, and that we are all tied together.”
It was an answer that may satisfy his constituency of mostly young and progressive Democrat voters. But Republicans prefer their candidates to wear their devotion on their sleeves. Senator Ted Cruz, the son of a born-again preacher, often cites II Chronicles 7:14, urging his supporters to pray daily for their country.
On 30 January it was his wife, Heidi, who said her husband was a servant of God. “Christianity and the Bible are at the centre of our home,” she said, to quiet murmurs of approval, “and the belief that we are here just for a short time to serve”.
Mr Trump is battling Mr Cruz for the devotion of evangelicals. The big surprise may prove to be that they privately consider Mr Trump a phony, but do not care.