Donald Trump continues to go where no recent candidate for president has gone before, plunging the Republican Party – and the nation – into another round in the tumultuous debate about immigration, national identity, terrorism and the limits of tolerance.

Trump’s call Monday for a ban on Muslims entering the United States marked a sudden and sizable escalation – and in this case one that sent shockwaves around the world – in the inflammatory and sometimes demagogic rhetoric of the candidate who continues to lead virtually every national and state poll testing whom Republicans favor for their presidential nomination.

Nothing in modern politics equates with the kind of rhetoric now coming from Candidate Trump. There are no perfect analogies. One must scroll back decades for echoes, however imperfect, of what he is saying, from the populist and racially based appeals of then-Alabama Gov. George Wallace in 1972 to the anti-Semitic diatribes of the radio preacher Charles Coughlin during the 1930s.

Historian David Kennedy of Stanford University said there are few comparisons, adding that, in branding an entire religious class of people as not welcome, Trump “is further out there than almost anyone in the annals of [U.S.] history.”

From the day he announced his candidacy in June, Trump has continually tested the limits of what a candidate can say and do with apparent political impunity. In that sense, he has played by a different set of rules. In the wake of his latest provocation, the question arises once again: Will this finally stop him? Everything to date suggests those who believe it should be tentative in their predictions.

Those already drawn to Trump have shown remarkable willingness to accept the worst and continue to support him. In reality, it will be another 60 days or more for any definitive answers to emerge. Only when voters begin to make their decisions in the caucuses and primaries that begin in February will the final verdict be delivered on the size and strength of the movement that has rallied behind him.

“This is a new campaign for a new century in which viral populism, most conspicuous on the GOP side, is the engine of our politics,” Ross Baker of Rutgers University noted in an email the day before Trump’s latest outburst. “Trump, above all others, has sensed this and is profiting from it. His reading of the anger and anxiety of the GOP primary electorate is positively seismographic. He senses what’s eating at people and, in his own bizarre way, is most attuned to the electorate of any of the hopefuls.”

GLOBAL CONDEMNATIONS

Even as Trump on Tuesday sought to soften slightly what he had said Monday, the condemnations mounted. He drew rebukes across the globe, from the leaders of two of America’s most important allies, Britain and France, to Syrian refugees in Lebanon’s Bekaa Valley. Rarely has a presidential candidate generated such alarm abroad as that now rising around the world aimed at Trump.

At home, the condemnations were just as swift and nearly universal. The harshest came from Martin O’Malley, the former Maryland governor seeking the Democratic nomination, who tweeted Monday that Trump “removes all doubt he is running for president as a fascist demagogue.”

Hillary Clinton sent out a tweet Tuesday that said in big letters, “Love trumps hate.” White House press secretary Josh Earnest said what Trump advocated Monday should disqualify him from ever serving as president, and he added that Republican candidates who refuse to say they would not support Trump as the party’s nominee also are disqualifying themselves.

Republican leaders, including House Speaker Paul Ryan, R-Wis., and most of Trump’s Republican rivals, stopped short of that. But though they have often been tentative in tangling with the master of the political counterpunch, most jumped quickly to state their disagreements with him.

Notable in his restraint was Texas Sen. Ted Cruz, who, while saying he did not agree with the proposal about blocking Muslims from coming into the country, also commended Trump for focusing attention on the need to secure the borders of the United States.

But as the political establishment rushed to criticize Trump, there is little doubt that he has tapped into a strain of anti-immigrant and anti-foreigner sentiment that has ebbed and flowed through American history. There are a number of antecedents over the past century that put Trump’s candidacy and the responses to it into historical context.

HISTORY REPEATS?

After World War I, a wave of immigration from Europe to the United States, coupled with fears of the spread of worldwide communism after the Bolshevik revolution, led to strikes, riots, violence, anarchism and ultimately a powerful backlash against immigrants. Then-Attorney General Mitchell Palmer led a series of infamous raids, rounding up suspected radicals and trying to deport them.

A rising nationalist and nativist strain fueled by the war and its aftermath eventually led Congress twice in three years in the early 1920s to enact strict new quotas on immigration, sharply limiting the influx of those fleeing a continent devastated by the war for opportunities in America.

In the past decade, illegal immigration from Mexico and Latin America has repeatedly emerged as a hot-button issue of America’s politics, playing out most prominently inside the Republican Party. Efforts to pass comprehensive immigration reform, advocated by then-President George W. Bush during his second term in office, faltered because of conservative resistance. Renewed efforts under President Barack Obama met similar opposition from conservatives in and out of Congress.

Fears of terrorism have now been layered on top of the issue of illegal immigration. Long-standing fears about Islamic State terrorism have intensified since the recent attacks in Paris and now the shootings in San Bernardino by a young California couple who had been radicalized but managed to conceal the transformation until it erupted last week.

Stanford’s Kennedy pointed to “inchoate, diffuse, free-floating anxiety” brought on by economic strains, the nation’s inability to extract itself from Middle East wars and a generally unsettled world as other causes for Trump’s appeal. He also noted that in contrast to times past, what once held extreme expressions in check no longer does.

“We’ve known for a long time that we’re just less trustful as a people,” he said. “We have less confidence in our major institutions and our leaders. … He gets denounced routinely when he does these things and everyone gets up and says this is not a voice we should listen to. But nobody has credibility on the other side. Nobody has the cultural authority to put this guy down. … All the condemnation in the world falls on deaf ears.”

What once might have seemed inconceivable in political debate has become acceptable, at least to a part of the population. That makes this moment a potential inflection point in the life of the country.

For the Republican Party, it highlights what has emerged as a deep split between the party elites and at least a portion of the rank-and-file. Next week’s debate in Las Vegas, the final Republican debate of this calendar year, will bring the candidates together on a stage in what has become the most virulent moment of the campaign. Trump will be under fire, but he has been there before and survived, even prospered. Will this moment prove any different?

Beyond that, however, Trump has brought into sharper focus important questions that will play out during the coming election year: What can be done to make Americans feel safer? What will impede or encourage recruitment by Islamic State terrorists? What does it mean to be an American? What kind of image does this nation project around the world?

Along with the rhetoric of Donald Trump, the stakes for 2016 have escalated dramatically.