Correction: A previous version of this post indicated that Madonna made her comments at a Sunday concert in Washington, D.C. She said the comments about President Obama at her Monday show at the Verizon Center.

Madonna, on Monday night at her Washington concert, had this to say about President Obama: “For better or for worse, all right, we have a black Muslim in the White House, okay?”

Actually, it’s not okay. It’s not okay for Obama, who is trying to appeal to an electorate in which 16 percent believe he is a Muslim. For many of those, “Muslim” is code for “black.” Madonna managed to sum up among the worst fears of the Obama campaign in two words.

Obama  is a Christian. He is constantly reminding us. He has to. He reminded  us at the lighting of the National Christmas tree last year. He reminded us at the Easter prayer breakfast. He reminded us at the 10th anniversary of the attacks on Sept. 11, 2001. Most recently, the president reminded us in his speech at the United Nations this week: “Like me, the majority of Americans are Christian, and yet we do not ban blasphemy against our most sacred beliefs.”

So why is it not sticking for that 16 percent?

Meanwhile, Mitt Romney’s religion problem is quite different. Everyone is clear that the GOP candidate is a Mormon. Some just don’t think that makes him a Christian. Although 74 percent of white evangelicals support Romney, a good number of those do not believe that Mormonism is a Christian religion. The most high-profile evangelical in the country, the Rev. Rick Warren from Saddleback Church in California, who gave the invocation at Obama’s inauguration, has said publicly that Mormons are not Christians.

“The key sticking point for evangelicals and actually for many is the issue of the Trinity. That’s the historic doctrine of the church that God is three in one. Not three Gods; one God in Father, Son and Holy Spirit. Mormonism denies that,” Warren said during an interview with ABC News in April.

Ralph Reed, founder of the Faith and Freedom Coalition, has begun outreach to 17 million evangelical GOP voters. He will try to convince this group that Romney’s conservative positions outweigh differences in their faiths.

So far, neither candidate has given a major speech on religion during this campaign. So should they? I have some advice for each of them.

Obama may think that he has brought it up enough, but it’s clearly not working. A speech on the subject would be a good idea.

Romney can’t win this battle. He needs to keep saying “God bless America” every chance he gets.   

In 2006, before Obama was president, he gave a major address at the Sojourners convention: “A Call to Renewal on Faith and Politics.”

He was astonishingly candid for a politician and very clear on his faith and his belief in the freedom of religion. He talked about how offended he was when one of his opponents for U.S. Senate said he was not a Christian. He related how he had not been religious when he went to Chicago but then joined the church. “You need to embrace Christ precisely because you have sins to wash away — because you are human and need an ally in this difficult journey.”

The speech was a tour de force. It was one thing to proclaim your belief in God, in fact it was obligatory in order to get elected, but it was not really expected that anyone would elaborate on the subject.

However, he was quick to add, that “nothing is more transparent than inauthentic expressions of faith.” And, he went on to say that “we are no longer just a Christian nation, we are also a Jewish nation, a Muslim nation, a Buddhist nation, a Hindu nation and a nation of nonbelievers.”

For his part, Romney, in his run for the presidency in 2007, made a speech about his faith that was criticized for being too generic. That led his advisers to steer him away from the subject in this campaign. In that 2007 speech, Romney spoke of being a Christian only once, without details: “I believe that Jesus Christ is the Son of God and the Savior of mankind. My church’s beliefs about Christ may not all be the same as those of other faiths. Each religion has its own unique doctrines and history. These are not bases for criticism but rather a test of our tolerance. Religious tolerance would be a shallow principle indeed if it were reserved only for faiths with which we agree.”

Romney didn’t fare well in that campaign, so people weren’t that concerned about his lack of specificity. But now he is the GOP nominee.And now there are many Mormons who feel strongly that Romney should speak more openly about his religion, that it would give voters a clearer idea of who he is. However, if Romney opened himself up to questions about his religion, it could be troublesome.

Answering questions based on the “unique doctrines and history” of the Mormon church simply opens up a Pandora’s box for Romney. Never mind that questions about any other religion would be just as controversial. It’s just that Mormonism is more recent and not as well known.

Obama is a different story.  For some reason, he can talk all he wants about being a Christian  and a determined group will never believe it. His Sojourners speech, as good as it was, was six years ago and has been long forgotten by voters. His occasional references to his Christianity don’t seem to resonate. Many on the right believe he is a Muslim; many on the left believe he is an atheist, as was his father, or agnostic, as was his mother.  His Sojourners speech was about freedom of and from religion in politics. He has repeatedly referenced Muslims, Jews, other faiths and no faiths in his talks. It’s not enough.

He needs to talk about why religion matters and how his Christianity has helped him through the extraordinarily stressful and dangerous four years in which he has been president. (He might convince a few of those undecideds that he is indeed a Christian. The election is still close. It matters.)

On the other hand, perhaps the 16 percent who believe that Obama is a Muslim and those evangelicals  who won’t vote for Romney because he is a Mormon will cancel each other out and it won’t make any difference.  You can’t count on it, though.

As for Madonna, she may have since corrected herself, but the damage is done.