Even with a lot of distrust of gay folks, Muslims, this group or that group throughout the 20th century, the single most distrusted group in America is atheists. And it’s damn hard to get elected POTUS if you’re a minority in anything - shit, we’ve only had two Presidents who have been divorced, one Catholic (given that a quarter of America is Catholic,) and one black dude. And every one of those guys was a Christian.
Is there any possible way to get an atheist in the White House? Assume no POD before January 1, 1900 and assume no ASB scenarios or Designated Survivor scenarios where the one dude to survive just happens to be an atheist. And no closet atheists, either - they must be openly atheist.
If it can’t be done, an agnostic or non-religious person may be acceptable. And try not to veer into current politics or who might have won in 2016 or in 2020.