My take: 'Atheist' isn’t a dirty word, congresswoman (CNN)

[Promethean]

2. The catch is Atheists mostly won't vote for someone just because they declare themself an Atheist

Atheists tend to have come to the decision to be an Atheist because of a great deal of thought and self reflection. Not because someone in a position of leadership told them to. So hearing a politician say "I am an Atheist" does not assure you votes from the Atheist population.

On the other hand among the religious the exact opposite tends to be true. There have been many polls that asked the straight question "Would you vote for someone you knew was an Atheist" and those polls by and large got a negative responses.