Because Mitt Romney is a Mormon (a member of the Church of Jesus Christ of Latter-day Saints), he is not a real Christian. (Here's Wikipedia's page on one of the right-wing "true" Christians who denounces Romney for not being enough like him. Note: This same man later endorsed Mitt Romney.)
And, for no apparent reason at all except hatred and bigotry and fear of someone who doesn't have a WASP-ish name, Barack Obama must not be a real Christian, either. (Here's Wikipedia's page on some of the Obama religion conspiracy theories.)
Mitt Romney and all Mormons are Christians. Clue # 1: the name of their church. Clue # 2: they believe that Jesus Christ is the Son of God and our Redeemer. You can learn more about their beliefs at the church's website. Clue # 3: they commit themselves to follow Christ's teachings, which they do, among other things, by taking care of poor people through official church programs and individually.
Barack Obama is a Christian. According to the Wikipedia page cited above, he was baptized into the United Church of Christ (UCC) denomination and formally joined it in 1988. He left left that congregation in 2008 because of the controversy over the Rev. Jeremiah Wright and has not become a formal member of any congregation since then, though he worships with a Southern Baptist pastor at Camp David. Also, Barack Obama wrote in "The Audacity of Hope" that although he was not raised in a religious household, his grandparents were "non-practicing Methodists and Baptists" and his mother, though she was "detached from religion," was "in many ways the most spiritually awakened person that I have ever known."
CONGRESS SHALL MAKE NO LAW RESPECTING AN ESTABLISHMENT OF RELIGION, OR PROHIBITING THE FREE EXERCISE THEREOF; OR ABRIDGING THE FREEDOM OF SPEECH, OR OF THE PRESS; OR THE RIGHT OF THE PEOPLE PEACEABLY TO ASSEMBLE, AND TO PETITION THE GOVERNMENT FOR A REDRESS OF GRIEVANCES.
Also: Madame L seems to remember that Christ himself taught us not to go around judging people and accusing them of being not as good as ourselves. For example (paraphrased from John 8: 1-7:
While Jesus was teaching the people, the lawyers and Pharisees brought to him a woman who had committed adultery. (Caught in the act!---and why wasn't the man she was committing adultery with not brought forward, too? Madame L does not know.)
They said, "Teacher, this woman was caught committing adultery. The Law of Moses says we should stone her. What do you say?"
Jesus stooped down and wrote something in the dust. (What did he write? Ah, if only we knew the answer to that question! Some people have suggested he was writing the names of those among the accusers who had committed adultery with the woman.)
Finally, he said, because they kept after him about it, "Okay, but the person who should throw the first stone at her has to be someone who has never himself sinned."
Strangely enough, they all left.
Madame L thinks the accusers of Barack Obama and Mitt Romney should look to their own Christian principles and behavior before they cast another stone at the presidential candidates.