In modern history, only one person has ever been an out atheist sitting in Congress. That was Rep. Pete Stark from California. He didn't admit he a "non-theist" until 2007. And he's no longer in Congress for unrelated reasons.
When Gallup asked Americans if they'd vote for someone of their own political party who happens to be an atheist, only 54% of people said yes. People were more likely to vote for a gay person or a Muslim.
That said, there are atheists who are out and hold statewide office, like Ernie Chambers, a state senator in Nebraska, and Juan Mendez, a state Rep. from Arizona.
So the point is clear: It's not impossible to be an atheist in public office, but you can pretty much count on one hand the number of atheists who hold real political power.
It raises some interesting questions: Can atheists win political office? Yes.
How do we do it?
Let me offer a few suggestions:
-- Go local: Atheists have a much better chance of getting elected to a local school board or city council. Once they get a reputation than goes beyond just their thoughts on God, they have a much easier chance of getting elected to statewide or even national office.
-- Make your values the story, not your beliefs: There are tons of awesome religious people who hold political office. And it doesn't bother me that they're religious because they don't make it a big deal. They vote the way I want them to vote. That's what should matter for all of us.
So if you're an atheist running for office, don't make that a focal point of your campaign. Don't hide from it, but focus on the issues, including the importance of church/state separation even for religious people.
-- Emphasize your Humanism over your atheism. It's a safer word that doesn't have the stigma attached to atheist, and it focuses on what you do believe, not what you don't.
-- Don't eat babies publicly: It rubs some people the wrong way.
-- Don't mention your atheism. This is admittedly sneaky. But it's strategic. If you're not already public about your atheism, hide it. Get elected based on your merits. If anyone asks you what religion you are, tell them your beliefs are a private matter. Then when you get elected, you can come out if you'd like. Or keep it hidden and just vote on bills that promote things like church/state separation or proper science.
The downside is you won't actually make a longterm difference in helping other atheists get elected.
-- Don't be afraid of losing: If you don't actually care whether you win or lose, then make your atheism as public as possible throughout the campaign. Herb Silverman, an atheist college professor from South Carolina, ran for Governor a couple of decades ago with the slogan, "the Candidate without a prayer." He had no real shot at winning, but he used the opportunity as a candidate to promote his views. And you know what? The next time an atheist candidate runs for office in South Carolina, it won't be as big of a story. Because that state's already seen it. And that'll make it easier for that atheist to win.