If there was an atheist candidate, no different from any other candidates, would you dismiss the possibility to vote for him/her on the sole basis that he/she was an atheist?
If a candidate was openly atheist, that would make me more inclined to vote for them. But not if they were obnoxiously vocal about it, because religious matters hold no place in politics -- and that includes atheism.
I'm sure there have been many atheists presidents. I wouldn't be surprised if a HUGE portion of them were, actually. The political game has always required using religion as a strategic advantage, sadly. Most politicians aren't genuine, they just know how to play the game well. Voting for anyone is always risky. There is no secure candidate who will genuinely live up to their word. If they did they'd be a terrible president lol. Listening to the people entirely is not smart.