Donald Trump: The most demagogic candidate in recent history?

Republican presidential candidate Donald Trump speaks at the Republican Jewish Coalition Presidential Forum in Washington, Thursday, Dec. 3, 2015.

AP

After his latest controversial proposal to bar Muslims from entering the U.S., Republican presidential front runner Donald Trump was admonished by scores of public figures on the left and the right, from Hillary Clinton to Dick Cheney.

The bombastic businessman finally seemed to push his demagoguery to a point that even those within his own party couldn't tolerate.

"I do not comment on what's going on in the presidential election -- I will take an exception today," House Speaker Paul Ryan, R-Wisconsin, said angrily one day after Trump announced his idea. "This is not conservatism. What was proposed yesterday is not what this party stands for, and more importantly, it's not what this country stands for."

"Trump's words are more explicitly bigoted than those of any leading American presidential candidate in recent memory. I cannot think of anything like it from an American political leader in the last 50 years," Princeton Professor Tali Mendelberg, author of "The Race Card: Campaign Strategy, Implicit Messages, and the Norm of Equality," told CBS News.

Among elected officials, there seems to be widespread agreement that Trump has crossed a line. So what does that mean for American politics? That depends on whether Trump is considered part of a larger trend of demagoguery that dates back to the Civil Rights era, or whether he's dubbed an outlier, argues Ian Haney-López, a professor at the University of California at Berkeley and author of "Dog Whistle Politics."

"The advent of Donald Trump may prove a watershed moment in American politics," Haney-López told CBS.

The bombastic front runner may help the Republican Party through the soul searching it tried to do after the 2012 election and help the American public at large consider its tolerance of divisive politics.

"Once you say, this is race baiting, this has been going on for too long... these are the sort of soul-searching questions one will hope Donald Trump will help the whole country to confront," Haney-López said. "This depends on seeing Trump as symptomatic of American politics rather than exceptional."

"Dog whistle" politics dates back to the early 1960's, when the Republican Party adopted the "Southern strategy" of appealing to segregationist white voters in the South who were previously aligned with the Democratic party.

Barry Goldwater, the GOP's presidential candidate in 1964, openly acknowledged he wouldn't win the support of African-Americans. He lost to President Lyndon Johnson, but he carried five states in the deep South -- and 1964 was the last year a Democratic candidate for president won the majority of the white vote in America.

Goldwater and GOP candidates thereafter put forward platforms of forced busing, law and order, and states' rights -- suggesting they could insulate white voters from minorities.

"The basic message of fear and resentment that undergirds all of this is there are good and decent people in society whose position is being threatened by dark and dangerous 'others,'" Haney-López said. "The Republican Party especially, but to some extent the Democrats, have essentially trained voters to expect and respond to this sort of fear-mongering."

Today the Republican Party draws around 90 percent of its support from white voters. But that doesn't mean that the GOP's strategy for electoral victory is one that is predicated on race-baiting. President George W. Bush made a point of rejecting bigotry, particularly after the September 11, 2001 terrorist attacks. Six days after the attacks, he visited the Islamic Center of Washington. Democrats have also been charged with race-baiting in recent history. Bill Clinton, for instance, ran his 1992 campaign on "dog whistle" themes of ending welfare as a "way of life" and cracking down on crime.

Attorney General Loretta Lynch is familiar with the dog-whistle coding in the context of crime. She talked about it in blunt terms 2007, when she was a U.S. attorney in New York. "Even with the statements as a DA, 'I'm going to be tough on crime,' there are people who take that and have taken it for years --because it has meant for year -- I'm going to be tougher on African Americans, depending upon the context, depending upon what else is being said in an election," Lynch said.

Some cases of race-baiting and demagoguery have been more egregious than others, such as the infamous 1988 "Willie Horton" ad, or Jesse Helms' 1990 Senate ad, "White hands." In 2000, Reform Party presidential candidate Pat Buchanan warned that immigrants are "taking our country away from us," while Newt Gingrich in 2010 objected to putting a mosque next to the World Trade Center site. "Nazis don't have the right to put up a sign next to the Holocaust Museum in Washington," Gingrich said. "We would never accept the Japanese putting up a site next to Pearl Harbor."

Even so, no other candidate in recent history has been as "explicitly exclusionary," Mendelberg said. "Trump-style rhetoric about any minority group is very rare," she said. "Some candidates do make racial appeals but they are much more subtle and implicit."

Mendelberg predicts that Trump is about to "lose big" because he's gone too far, for public figures and voters.

"Americans have a strong norm of racial and ethnic equality when it comes to public speech," she said. "The norm has probably weakened over the past couple of decades with the rise of talk radio and social media. People feel more free now to make explicit derogatory comments. But the norm still holds for public figures. Trump is weakening that norm, but now that he has gone so far, even right-wing Republican leaders are excoriating him."

Yet so far, Trump has held fast to a dedicated group of supporters. After months of pushing the envelope further and further -- with inflammatory comments about Mexicans, the spread of misinformation about crime and African-Americans, and his stance on Muslims coming to America -- he has remained the lead Republican presidential candidate.

Haney-López suggests that Trump's appeal is holding because he hasn't quite veered into the realm of outright racism. Coded language, he said, "is helping the people who are responding positively to Trump's message to believe they are fundamentally good people, that they are not racist -- that there's a real crisis that Trump's articulating," he said. Trump supporters, he continued, are by and large "good, decent people who are dead set against racism -- but they understand racism very narrowly."

In an interview with Boston radio station WRKO on Wednesday, Trump argued that his anti-Muslim policy proposal isn't bigoted.

"This isn't about religion," he said. "This is about safety... These are people coming from outside. We are at a point in this country where we just can't afford to make mistakes. You will have a lot of problems in the future. We just can't have it. This has nothing to do with religion."