When Republican Ben Carson declared Muslims unfit to be president, he crossed a line that historians say no major White House hopeful has breached since the 1940s — openly expressing prejudice.
Carson is not the first to appeal to voter bias, but he broke with a timeworn tradition of using coded language to avert any political backlash.
"I would not advocate that we put a Muslim in charge of this nation," Carson said on NBC's "Meet the Press" last week. "I absolutely would not agree with that."
With that, Carson highlighted the recent coarsening of public discourse in "a different kind of world where people take in stride the strident, racist things that are said," said Norman Ornstein, coauthor of "It's Even Worse Than It Looks: How the American Constitutional System Collided With the New Politics of Extremism."
"I think it's part of the Internet age, but also a media world where there are so many outlets, and so many voices, and so much cacophony, that to cut through you need shock value," Ornstein said.
Carson's disparagement of Muslims came after months of derogatory remarks about women and Mexicans by rival Donald Trump, who nonetheless has remained the front-runner for the party nomination. Carson is in second place, polls show.
Some Republican leaders, already fretting over Trump's insults, fear that Carson's denigration of Muslims will further damage the party's efforts to expand its base beyond older conservative white voters.
Civil rights groups and some of Carson's Republican rivals denounced the retired neurosurgeon, but he stands little risk of harm in the primaries. A 2013 survey by the nonpartisan Pew Research Center found that nearly two-thirds of white evangelical Protestants — a key group for Carson, a Seventh-day Adventist — believe Islam is more likely than other religions to encourage violence.
Historian Thomas S. Kidd, author of "American Christians and Islam," said Carson was capitalizing on fear of Muslim terrorists. "But then to turn it into a blanket statement that Muslims in general can't be full participants in the life of the republic — I do think that's significant, and it's alarming," Kidd said.
Carson campaign manager Barry Bennett said the comments were justified because Islam calls for killing gay people, and that's incompatible with the Constitution. (Muslim clerics say that's untrue. The Constitution says that "no religious test shall ever be required as a qualification to any office or public trust under the United States.")
Bennett also said that as an African American, Carson himself "dramatically expands the appeal of the Republican Party."
Carson later told CNN that a Muslim would "have to reject the tenets of Islam" to be president.
Presidential candidates typically take pains to avoid showing religious bias. When Republican Mitt Romney, a Mormon, ran in 2008 and 2012, hostility toward his faith among some evangelicals posed a challenge. One of his 2008 opponents, Republican Mike Huckabee, a Southern Baptist minister, apologized to Romney after asking a reporter, "Don't Mormons believe that Jesus and the devil are brothers?"
In 1960, Democrat John F. Kennedy, a Catholic, had to reassure Protestants that he would not take orders from the Pope. But his main opponents, Hubert Humphrey in the primaries and Republican Richard Nixon in the general election, avoided the topic.
"Humphrey certainly didn't say anything like what Carson said," Kennedy biographer Robert Dallek recalled. Nixon didn't need to stoke doubts about Kennedy's faith because "there were plenty of people who were doing it for him," he said.
Since World War ll, historians say, the presidential candidate most openly prejudiced was Strom Thurmond, whose racism was unvarnished when he ran in 1948 as a Dixiecrat.
"There's not enough troops in the Army to force the Southern people to break down segregation and admit the nigra race into our theaters, into our swimming pools, into our homes, and into our churches," the South Carolinian told one crowd.
Alabama Gov. George Wallace was nearly as direct in his 1963 inaugural speech, pledging "segregation today, segregation tomorrow and segregation forever." But in his first run for president in 1964, then-Democrat Wallace was more guarded in appealing to whites outside the South at a time when many were uneasy about a new housing discrimination ban that would enable blacks to move into their neighborhoods.
"You may want to sell your house to someone with blue eyes and green teeth, and that's all right," he told a Maryland audience. "I don't object. But you should not be forced to do it. A man's house is his castle."
"Everyone assumed he was racist," said historian Dan T. Carter, author of "From George Wallace to Newt Gingrich: Race in the Conservative Counterrevolution." "So to use explicitly racist language, or language like Carson used talking about Muslims, would have just confirmed what people secretly thought, and would have been very damaging to his candidacy."
After Romney's loss in 2012, Republicans vowed to work harder to attract minority voters. The Republican National Committee released a scathing post-mortem saying that "many minorities wrongly think that Republicans do not like them or want them in the country."
But Trump and Carson are benefiting from the uneasiness of many working-class whites as the nation grows more diverse.
Their rhetoric is alarming party strategist Henry Barbour, a coauthor of the RNC report.
"When you say a Muslim's not fit to be president of the United States, you're a whole lot more than off message," he said. "We need to stand on principle, but we don't need to try to run folks off because they have different backgrounds than some traditional Republicans."