LONDON >> Mass shootings by Islamist militants. Migrants crashing borders. International competition punishing workers but enriching elites.

Across the Western world, a new breed of right-leaning populists from Donald J. Trump in the Republican presidential primary to Marine Le Pen in France and Viktor Orban in Hungary are surging in popularity by capitalizing on a climate of insecurity unrivaled since the period after the First World War.

Many of them — led this week by Trump — have made headlines in recent months by railing against Muslim immigrants, calling them a threat to public safety and cultural identity. Left-leaning critics have compared their nativist and nationalist rhetoric to the fascists of the early 20th century because some riding the populist wave — like the Freedom Party in Austria or Golden Dawn in Greece — have neo-Nazi roots.

Unlike earlier right wing movements, though, these populists disavow the overt racism, militaristic rhetoric and associations with fascism that previously scared away many mainstream voters.

Before the recent terrorist attacks or the European migrant crisis cast a spotlight on Muslim immigration, the populists had built support primarily as trade protectionists or economic nationalists appealing to hard-pressed working-class voters who felt disaffected from their country’s established parties and political elites. And, for the first time in nearly a century, established parties across Europe and the United States are struggling to fend off the populist insurgents as their competition pulls the mainstream further to the right.

“What you are seeing here is quite a radical shift,” said Roger Eatwell, a political scientist at the University of Bath who studies right-wing parties.

Le Pen is the best-known figure from more than a dozen right-leaning populist parties across Europe that have scored big gains during the last two years. This week, her National Front party won the largest share of the vote in the first round of regional elections in France, with 30 percent, making her a contender for the presidency in 2017. She campaigns against what she calls the Islamization of France and has compared Muslims praying in French streets to the Nazi occupation.

But Le Pen fuses her cultural chauvinism with appeals to the economic anxieties of working or lower-middle class voters who — like their counterparts across Europe — have suffered from high unemployment, stagnant wages and growing income inequality, especially since the financial crisis of 2008.

“They are pulling out all the stops for the migrants, the illegals, but who is looking out for our retirees?” Le Pen asked in a recent campaign appearance. “They are stealing from the poor to give to foreigners who did not even ask our permission to come here.”

Trump on Monday evoked comparisons to Le Pen and her European counterparts with his call to close American borders to all Muslims “until our country’s representatives can figure out what the hell is going on.”

Le Pen said that was too much for her, perhaps in part because she feared jeopardizing the progress she had made in shedding her party’s previous image as racist and anti-Semitic.

“Seriously, have you ever heard me say something like that?” she asked on Thursday when questioned about Trump’s comments during a television interview. “I defend all the French people in France, regardless of their origin, regardless of their religion.”

Others in Europe’s right-leaning populist parties, though, are applauding Trump for breaking with what they call the multiculturalist orthodoxy of dominant political elites.

“He is a phenomenon,” said Gawain Towler, a spokesman for the U.K. Independence Party, a right-leaning populist party here.

“They are glad that somebody is saying things along these lines, and that is the same reason why you are now seeing significant support for political groups on the continent of Europe — whether in France, or Denmark or Finland or the others — who do not just repeat the shibboleths of the old establishment,” Towler said.

In all the countries, he said, “the same people have been governing for a long time and they have completely let down the indigenous inhabitants, particularly at the lower end of the economic spectrum.”

Streaks of nativism have surfaced in Western Europe since it first welcomed waves of immigrants from former colonies in the middle of the last century, with thousands of Indians, Jamaicans and others arriving in Britain.

But only in the last two decades — with the growing numbers of people arriving from Asia, the Middle East and Africa — has nativist sentiment in Europe become as prominent as it is in the United States, where immigration is central to the national experience.

In addition, the voices that have taken up the cause of defending national borders and traditional cultures against immigration and other perceived threats are now coming for the first time from populist voices outside the political establishment. One exception is Hungary, where Prime Minister Viktor Orban is a right-leaning populist who leads an establishment party, pulled further rightward by competition from the more extreme Jobbik party.

Links that once tied parties to their constituencies — Christian Democrats to Catholic churches, for example, or Social Democrats to labor unions — have frayed. Changes in mass media have made celebrities of some political leaders while devaluing some traditional party organizations.

But at the same time, establishment parties on the left and right alike have also largely failed to provide solutions for the problems that most vexing to working-class voters: income stagnation, insecurity and inequality in an age of technological change and global competition.

A poll conducted in Europe last spring by the Pew Research Center found extraordinary gloom about the state of their economies: Sizable majorities in a half-dozen countries expected children to be worse off than their parents. That pessimistic view was held by 58 percent of the German respondents, two-thirds of the British, and 85 percent of the French.

A Pew poll in the United States around the same time found that two-thirds of respondents believed government polices since the 2008 financial crisis had primarily benefited the wealthy instead of the middle class or the poor — a view held by 70 percent of those making less than $75,000 a year and by 55 percent of Republicans.

Until this year, economic anxieties appeared to be the main fuel propelling the growth of upstart populist parties across Europe, including a few on the left as well as the right. They campaigned as Euroskeptics, assailing the transfer of decision-making to the distant European Union authorities in Brussels and denouncing the cost of bailouts or the pain of austerity measures.

The populists saw big gains in a dozen countries during the European parliamentary elections in the spring of 2014 and led the polling in Britain and France before the migrant crisis or recent terrorist attacks.

“The financial crisis and the eurozone crisis and all the problems the EU was having — they all created fears that these parties were able to channel very well,” said Ruth Wodak, a professor at Lancaster University in England and author of “The Politics of Fear: What Right-Wing Populist Discourses Mean.”

In each case, the core constituencies of the new right-wing parties were working-class men. “These are voters who feel economically left behind, under threat from immigration and rapid social change, and cut adrift from established politics,” said Matthew J. Goodwin, a political scientist at the University of Kent who studies the right.

Trump, too, draws much of his support primarily among voters without a college education. The latest New York Times/CBS News nationwide poll showed that Trump had the support of 40 percent of Republican voters without a college degree. He had the support of 26 percent among those with a college degree.

The poll was largely taken before his statement on Monday afternoon proposing to temporarily bar Muslims from entering the United States.

Unlike his populist counterparts in Europe, Trump does not come out of any movement or ideology, nor does he have much history in the Republican Party.

But he has combined his signature themes about the perils of immigration with stances that try to address the economic anxieties of working people as well. He has accused hedge funds of “getting away with murder,” calling them “guys that shift paper around and get lucky.” And he has denounced free-trade deals, vowed to put tariffs on imports and pledged to stop immigrants or foreign workers from competing for jobs.

Pat Buchanan, who ran his own right-leaning populist presidential campaigns in the United States for three elections beginning in 1992, said in an interview that he recognized many of the cultural and economic themes he employed in the strategies of Trump, Le Pen, and the others around Europe. Their movements were manifestations of the same global forces, he argued.

“Nationalism and tribalism and faith — these are the driving forces now and they are tearing apart transnational institutions all over the world,” he said.

It all reminded him, he wrote in a follow-up email, of a line from the “The Second Coming,” by W.B. Yeats: “Things fall apart; the center cannot hold.”