Intolerance is ugly. It has no place in our society. And yet it persists, in virulent strains that refuse to die and become a pox on all of us.

The anti-Muslim sentiment festering in this country is one such strain. And it has burst into the open, infecting the 2016 presidential race, thanks to Republican candidates Ben Carson and Donald Trump. First, Trump declined to correct or condemn a supporter who asserted at a New Hampshire campaign rally that Muslims are a "problem," that President Barack Obama is a Muslim, and that Muslims are being trained in camps to kill "us." Trump's pathetic response was that he is "going to look at that." Three days later, Carson flatly said on national TV that Muslims are not fit to be president because their religion is not consistent with the Constitution.

Were they responding to dropping poll numbers by blowing a crude dog whistle to rally the faithful, those who are desperately trying to hang on to the old order? Or are their beliefs genuinely held?

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It doesn't matter.

What they said was repellent, and should be called out. Any candidate of any party who did not condemn them also is culpable. Even Rep. Peter King, who has relentlessly criticized Muslim leadership in this country, said Carson was wrong. "A Muslim has every right to run for president and be president," King said in a television interview. "Don't tarnish the whole community."

Carson's statement played to rank prejudice by conjuring images associated with radical Islam -- the Twin Towers falling on 9/11, Islamic State beheadings in the Middle East -- and was a departure from his 2011 book that called it "absurd" to paint every Muslim with the same philosophical brush. He might have proved he is unfit to be president because he doesn't understand the U.S. Constitution, which bans the use of religion as a litmus test for public office. His comment ignored the scores of Muslims in elected office nationwide, including two members of Congress, and the many serving in our armed forces. And it added to a climate in which a 14-year-old Muslim boy in Texas bringing to school a homemade clock to show his teacher can be arrested and taken away in handcuffs for supposedly making a fake bomb.

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Fifty-five years ago, it was John F. Kennedy fighting the sentiment that a Catholic couldn't be president, then voiced by the Rev. Norman Vincent Peale, the prominent Protestant pastor and publisher. In 1928, New York Gov. Al Smith faced the same discrimination during his run for president. In 2012, Mitt Romney faced suspicions about a Mormon running for president.

Now there's a new religious target. Now it's Carson telling Muslim boys and girls that one of the dreams that defines this country -- that anyone in America can grow up to be president -- is closed to them. It's profoundly sad that 239 years after this country was founded, we still are closing the doors of opportunity our Founding Fathers flung wide open.

We must understand that it is not one's religion but one's willingness to uphold the Constitution that is a qualifier for elected office. Some people who profess to love our country best have not figured that out yet.