What is a Christian?

For every time that Coulter slips a "B. Hussein Obama" into the discussion with Neil Cavuto, he simply slips in a little bit of "I pray to Jesus every night" at his next campaign stop. Partisan sides are already disinclined to believe the other anyway, and the useless rhetorical exercise repeats itself all over again the next day.

. . . The bigger danger in the controversy is that it is giving cover for the candidate to continue to spread the fraudulent idea that he is, in fact, a Christian.

This is from Kevin McCullough's latest article.

If Obama wins the nomination (as I hope he does), this will be something we will hear nearly constantly for the next 8 months. Conservatives have already set lines of attack on Clinton, but with Obama they have to pick new attacks. And one line of attack will be an attack on his Christianity. We will hear that he's not really a Christian over and over again.

But why does McCullough get to decide who is a Christian and who isn't? And what are the odds that he will judge any Democrat, ever, a Christian?