He is allowed to say such things…
Check it out:

Republican Wisconsin Gov. Scott Walker may be catching flak from the media glitterati for not definitely affirming his belief that President Barack Obama is a practicing Christian, but he isn’t the only one who has questioned the sincerity of the president’s faith.

During an appearance last June on Comedy Central’s “The Daily Show,” liberal comedian and mega-Obama campaign donor Bill Maher said he was confident that the president was really an atheist.

“He’s a drop dead atheist,” Maher, who himself is an atheist, said of Obama.