While the trend over time is encouraging, it remains the case that an atheist candidate is automatically disqualified by 46% of the voters, making it impossible for any such candidate to win. Atheists are disqualified by more voters than Muslims, and Islam is probably the least popular religion in this country right now.
Here's the poll described in the Huffpo article:
http://www.gallup.com/poll/155285/Atheists-Muslims-Bias-Presidential-Candidates.aspx
You have to wonder what is going on with the electorate when both gays/lesbians and Muslims - 2 groups who face considerable prejudice in our society - fare better than atheists.