Not so long ago it was foolish to think that the U.S. would elect an atheist president, but this year we did it. That is the good news, another glass ceiling has been broken. The bad news is that it was Donald Trump. I know that there are many people who might disagree with this observation but why? Atheism is the default state of being. When a person is born, he is not Christian or Hindu. He is just a person with no beliefs at all. He is in his default state. Christianity (and all other religions) are learned and cultural. This is why 88% of people have the same religion as their parents.
That said, a person (or his parent) has to choose to be a subscriber to a religion. Until that point, he has no religion. Donald Trump paid a little lip service to the Christian right, but he had to do this of course. He is not an active member of any church. He says he travels too much to attend church. He openly said he has never asked God for forgiveness. When asked, “What is your favorite bible verse?”, he has no answer. I think that is pretty safe to say that he has no religion at all. This was blatantly obvious in his campaign, but evangelicals choose to ignore it. They despised Hillary so much that they would have voted for Satan himself if given the chance. I do not think that this is a stretch.
Undoubtedly there is and have been atheist members of congress. After all, everyone has to pay lip service to faith and all. There is no better way to get money from people than to go to church with them. All you have to do is look at Jim Bakker and Jimmy Swaggart. They can suck more money out of poor people than Herbalife. However, they are not true believers. Nobody doubts the sincerity of Jimmy Carter. He actually practiced what he preached. Any non-religious person who has no emotional investment in that system can plainly see who is scamming the willfully gullible.