WASHINGTON — The comparison was inflammatory, to say the least. Former Gov. William F. Weld of Massachusetts equated Donald J. Trump’s immigration plan with Kristallnacht, the night of horror in 1938 when rampaging Nazis smashed Jewish homes and businesses in Germany and killed scores of Jews.
But if it was a provocative analogy, it was not a lonely one. Mr. Trump’s campaign has engendered impassioned debate about the nature of his appeal and warnings from critics on the left and the right about the potential rise of fascism in the United States. More strident opponents have likened Mr. Trump to Adolf Hitler and Benito Mussolini.
To supporters, such comparisons are deeply unfair smear tactics used to tar conservatives and scare voters. For a bipartisan establishment whose foundation has been shaken by Mr. Trump’s ascendance, these backers say, it is easier to delegitimize his support than to acknowledge widespread popular anger at the failure of both parties to confront the nation’s challenges.
But the discussion comes as questions are surfacing around the globe about a revival of fascism, generally defined as a governmental system that asserts complete power and emphasizes aggressive nationalism and often racism. In places like Russia and Turkey, leaders likeVladimir V. Putin and Recep Tayyip Erdogan employ strongman tactics. In Austria, a nationalist candidate came within three-tenths of a percentage point of becoming the first far-right head of state elected in Europe since World War II.
In Hungary, an authoritarian government has clamped down on the news media and erected razor wire fences to keep out migrants. There are worries that Poland may follow suit. Traditional parties in France, Germany, Greece and elsewhere have been challenged by nationalist movements amid an economic crisis and waves of migrants. In Israel, fascism analogies by a former prime minister and a top general have again inflamed the long-running debate about the occupation ofPalestinian territories.
“The crash of 2008 showed how globalization creates losers as well as winners,” said Mark Leonard, the director of the European Council on Foreign Relations. “In many countries, middle-class wages are stagnant and politics has become a battle over a shrinking pie. Populists have replaced contests between left and right with a struggle between cosmopolitan elites and angry nativists.”
That dislocation may not lead to a repeat of Europe in the 1930s, but it has fueled a debate about global political trends. There is a tendency at times to try to fit current movements into understandable constructs — some refer to terrorist groups in the Middle East as Islamofascists — but scholars say there is a spectrum that includes right-wing nationalism, illiberal democracy and populist autocracy.
“On a world level, the situation that affects many countries is economic stagnation and the arrival of immigrants,” said Robert O. Paxton, a professor emeritus at Columbia University and one of the most prominent scholars of fascism. “That’s a one-two punch that democratic governments are having enormous trouble in meeting.”
Mr. Trump dismisses the labels used by those like Mr. Weld, a longtime Republican now mounting a quixotic campaign for vice president as a Libertarian. “I don’t talk about his alcoholism,” Mr. Trump said through a spokeswoman, “so why would he talk about my foolishly perceived fascism? There is nobody less of a fascist than Donald Trump.” (Mr. Weld, who in the 1990s reportedly appeared in public a few times having had too much to drink, declined to respond: “I’ll let that ride.”)
Americans are used to the idea that other countries may be vulnerable to such movements, but while figures like Father Charles Coughlin, the demagogic radio broadcaster, enjoyed wide followings in the 1930s, neither major party has ever nominated anyone quite like Mr. Trump.