Attacking someone for “look[ing] like a Muslim,” on the other hand, arouses barely any controversy. Some liberal blogs condemned O’Reilly’s comments, but it’s unlikely that he will apologize and unthinkable that he’ll resign.

In conservative circles today, in fact, high-profile expressions of anti-Muslim bigotry are as routine as anti-black or anti-Jewish slurs were a half-century ago. In 2011, Republican presidential candidate Herman Cain vowed not to appoint a Muslim to his cabinet. Far from crippling his candidacy, the comment preceded his meteoric (if short-lived) ascent into the lead in national polls. Newt Gingrich traveled the country warning, “I believe Shariah is a mortal threat to the survival of freedom in the United States.” At its 2012 national convention, the GOP featured a Catholic priest, a rabbi, an evangelical minister, a Sikh, a Greek Orthodox archbishop, and two Mormon leaders but, conspicuously failed to invite an imam.

It’s not just conservative elites. A 2012 poll for the Arab American Institute found that while 29 percent of Democrats hold an “unfavorable” view of Muslims, among Republicans it's 57 percent. In 2013, two researchers at Carnegie Mellon sent out the resumes of a fictitious Christian and Muslim job applicant with the same credentials. In the 10 states where Barack Obama recorded his highest vote percentage, the two applicants received interview requests at the same rate. In the 10 states where Romney did best, by contrast, the Christian applicant was more than eight times more likely to be asked for an interview.

It would be comforting to believe this is merely a holdover from 9/11, and anti-Muslim bigotry will fade as we move further from that trauma. But according to the Arab American Institute poll, Republicans are 17 points more likely to dislike Muslims than they were in 2003 (although the numbers were even higher in 2010). Between 2002 and 2013, according to the Pew Research Center, the percentage of Republicans who said Islam is more likely than other religions to encourage violence rose 29 points.

Even as public tolerance for most other forms of bigotry declines, hostility to Muslims has actually grown, despite the winding down of America’s wars in Iraq and Afghanistan. In fact, the rise may be partially due to the end of those wars. After 9/11, George W. Bush told Americans that although we were fighting “bad Muslims” (al-Qaeda) “good Muslims”—who constituted the large majority—would embrace our invasions.

It hasn’t worked out that way. My hunch is that faced with the realization that many Iraqis and Afghans hated America’s occupation of their countries, Democrats have been more likely to blame the U.S. for starting those wars in the first place. According to polls, large majorities of Democrats now see both Iraq and Afghanistan as mistakes. Republicans don’t. For Republicans, I suspect, America’s problems in Iraq and Afghanistan say less about us than about them. They prove that Bush was wrong: Most Muslims really are our enemy. Otherwise, why would they oppose our efforts to make them free?