Often in fiction, whenever the President of the United States enters the scene as a bit player, it’s a black man or a woman just to emphasize how different the fictional world is from the current one. This is especially prevalent when the work is set 20 minutes into the future like a disaster movie.
However, polls have that atheists are the most unelectable minority in the US. Has there been any work of fiction that casts an explicitly atheist president? I can’t think of any off the top of my head.