Actually I would have thought the percentages were higher!
Roughly 1/2 of America supports Obama, so they are clearly not believing Christians (some are perhaps Christian in name only).
And not all those who voted against Obama are Christians.
Ergo, more than half of believing Christians believe Obama is the anti-Christ (and some of those who say they don't think he is the anti-Christ might be withholding the truth about how they really feel).