During his speech in Phoenix on Tuesday night, Donald Trump spat out the nickname “antifa,” short for “anti-fascist” but also a reference to a particular strand of aggressive left-wing activism. In Mr. Trump’s telling, the presence of antifa activists during the violence in Charlottesville, Va., this month was evidence that the far left is just as violent as the far right: “You know, they show up in the helmets and the black masks, and they’ve got clubs and they’ve got everything.” 
 
 Surrogates have aped Mr. Trump’s “blame both sides” rhetoric; overnight, antifa — and its assumed synonym, “alt-left” — have become right-wing shibboleths, right there with “social justice warrior” and “liberal snowflake.” In truth, there is no symmetry between either “alt-right” and either “antifa” or “alt-left.” Antifa is the backlash to the backlash, a defensive response to the growing presence of right-wing extremism. 
 
 But that doesn’t mean we shouldn’t worry. Because antifa groups are willing to use force when needed, provoking them can trigger a self-fulfilling prophecy. 
 
 So far, there is a fearful asymmetry between the far right and antifa: Over the decade ending in 2016, estimates of the percentage of politically motivated killings committed by right-wing extremists range from 73 to 92 percent, according to the conservative Daily Caller. Despite the spurious rhetoric of equivalency, supporters of antifa have, to date, killed no one. 
 
 Who are the antifa, then? They do not advocate a positive doctrine, racial or otherwise. Some supporters consider themselves (as Mr. Trump accurately said) anarchists, some Marxists of different stripes; others don’t care much what you call them. There is no national antifa organization; most organized groups are local, concentrated in Texas and the Northwest. There’s not even a consensus among adherents as to whether to pronounce the term AN-tee-fah or an-TEE-fah. They aim to confront, expose, shame — and sometimes convert — white supremacists. 
 
 It’s action and style, not doctrine, that unites them. In a world where racist movements form an archipelago of brown-walled islands — with friendly governments in power in Hungary, Poland and the United States — antifa fights back, and although not murderous, is not squeamish about its means. Considering normal political action hopeless, some antifa activists claim inspiration from the left-wing paramilitaries of Weimar Germany and from the Black Panther Party. They are aware of, or unimpressed by, the fact that when Hitler came to power, he crushed the left-wing militias, and that, having branded themselves as gun-toters, the Panthers became targets of convenience for police and federal agents. 
 
 In antifa circles, the theme of hypermasculine bravado is often right out front, and unsurprisingly, a large majority of the antifa camp are men. Muscularity is prized. After last weekend, one anarchist from Charlottesville described himself as “a blue-collar person, with a job, family, and responsibilities” who “did not behave peacefully when I saw a thousand Nazis occupy a sizable American city. I fought them with the most persuasive instruments at hand, the way both my grandfathers did. I was maced, punched, kicked, and beaten with sticks, but I gave as good as I got, and usually better.” 
 
 Few antifa groups wear masks or carry firearms, though in a street confrontation, especially in an open-carry state like Virginia, where the Charlottesville police did not separate rival groups, a few firearms go a long way. One group calling itself Redneck Revolt (“Putting the Red Back in Redneck”) displayed rifles in Charlottesville and took credit — witnesses agree — for protecting the larger crowd of antifa demonstrators. 
 
 Many liberals and leftists think they taint the overwhelmingly nonviolent anti-Trump resistance movement and play into Mr. Trump’s hands. No less a left-wing eminence than Noam Chomsky calls the antifa “a minuscule fringe of the left” and “a major gift to the right.” Mr. Chomsky considers them unprincipled, outnumbered and outgunned, as well as a distraction from practical tasks. 
 
 But many antifa activists do not think strategically about whom they alienate. They are convinced that the hour for normal politics has passed, and let the chips fall where they may. 
 
 What happens now? Antifa, riding a vastly larger anti-Trump wave, will probably grow. So does the potential for armed clashes, especially in open-carry states. If the police do not act astutely, armed showdowns could develop. 
 
 Right-wing paramilitaries have been training for years, descendants of the militias of the 1990s, reawakened by their horror that a black man had been elected president of the United States. They have uniforms, insignia, traditions and, not least, stockpiles of weapons. Not only do they thrive under a friendly president, but open-carry states like Virginia enable them to intimidate peaceful assemblies. For the racist right, violence is not only a tactic, it is a calling card. 
 
 Taking a cue from the president, right-wing militias now have antifa in their sights. Charlottesville was only the most visible confrontation; the two sides have been clashing for months. “We bullied antifa,” a website called Men of the West crowed in May, after an ex-Marine smashed an antifa leader head first into a lamppost for touching his flag during a confrontation in Austin. 
 
 Antifa depends far less on guns for its sense of identity. If effectively contained and self-contained, many of its supporters would likely return to the kind of nonviolent left-wing, anti-racist organizing that they were involved in before Mr. Trump rejuvenated the nationalist right with fire and fury. But for the foreseeable future, the counter-backlash is not going away. More Charlottesvilles, or worse, may be coming, too. ||||| Who are the antifa, then? They do not advocate a positive doctrine, racial or otherwise. Some supporters consider themselves (as Mr. Trump accurately said) anarchists, some Marxists of different stripes; others don’t care much what you call them. There is no national antifa organization; most organized groups are local, concentrated in Texas and the Northwest. There’s not even a consensus among adherents as to whether to pronounce the term AN-tee-fah or an-TEE-fah. They aim to confront, expose, shame — and sometimes convert — white supremacists. 
 
 It’s action and style, not doctrine, that unites them. In a world where racist movements form an archipelago of brown-walled islands — with friendly governments in power in Hungary, Poland and the United States — antifa fights back, and although not murderous, is not squeamish about its means. Considering normal political action hopeless, some antifa activists claim inspiration from the left-wing paramilitaries of Weimar Germany and from the Black Panther Party. They are aware of, or unimpressed by, the fact that when Hitler came to power, he crushed the left-wing militias, and that, having branded themselves as gun-toters, the Panthers became targets of convenience for police and federal agents. 
 
 In antifa circles, the theme of hypermasculine bravado is often right out front, and unsurprisingly, a large majority of the antifa camp are men. Muscularity is prized. After last weekend, one anarchist from Charlottesville described himself as “a blue-collar person, with a job, family, and responsibilities” who “did not behave peacefully when I saw a thousand Nazis occupy a sizable American city. I fought them with the most persuasive instruments at hand, the way both my grandfathers did. I was maced, punched, kicked, and beaten with sticks, but I gave as good as I got, and usually better.” 
 
 Few antifa groups wear masks or carry firearms, though in a street confrontation, especially in an open-carry state like Virginia, where the Charlottesville police did not separate rival groups, a few firearms go a long way. One group calling itself Redneck Revolt (“Putting the Red Back in Redneck”) displayed rifles in Charlottesville and took credit — witnesses agree — for protecting the larger crowd of antifa demonstrators. 
 
 Many liberals and leftists think they taint the overwhelmingly nonviolent anti-Trump resistance movement and play into Mr. Trump’s hands. No less a left-wing eminence than Noam Chomsky calls the antifa “a minuscule fringe of the left” and “a major gift to the right.” Mr. Chomsky considers them unprincipled, outnumbered and outgunned, as well as a distraction from practical tasks. ||||| This column has been updated. 
 
 Last weekend in Berkeley, Calif., a group of neo-communist antifa — “anti-fascist” — thugs attacked peaceful protesters at a “No to Marxism in America” rally, wielding sticks and pepper spray, and beating people with homemade shields that read (I kid you not) “No Hate.” The Post reports how one peaceful protester “was attacked by five black-clad antifa members, each windmilling kicks and punches into a man desperately trying to protect himself.” Members of the Berkeley College Republicans were then stalked by antifa goons who followed them to a gas station and demanded they “get the [expletive] out” of their car, warning, “We are real hungry for supremacists and there is more of us.” 
 
 The organizer of the anti-Marxism protest is not a white supremacist. Amber Cummings is a self-described “transsexual female who embraces diversity” and had announced on Facebook that “any racist groups like the KKK [and] Neo Nazis . . . are not welcome.” The protest was needed, Cummings said, because “Berkeley is a ground zero for the Marxist Movement.” 
 
 As if to prove Cummings’s point, the antifa movement responded with jackboots and clubs — because their definition of “fascist” includes not just neo-Nazis but also anyone who opposes their totalitarian worldview. 
 
 And let’s be clear: Totalitarian is precisely what they are. Mark Bray, a Dartmouth lecturer who has defended antifa’s violent tactics, recently explained in The Post, “Its adherents are predominantly communists, socialists and anarchists” who believe that physical violence “is both ethically justifiable and strategically effective.” In other words, they are no different from neo-Nazis. Neo-Nazis are the violent advocates of a murderous ideology that killed 25 million people last century. Antifa members are the violent advocates of a murderous ideology that, according to “The Black Book of Communism,” killed between 85 million and 100 million people last century. Both practice violence and preach hate. They are morally indistinguishable. There is no difference between those who beat innocent people in the name of the ideology that gave us Hitler and Himmler and those who beat innocent people in the name of the ideology that gave us Stalin and Dzerzhinsky. 
 
 Artist and activist Bree Newsome says that, like the rise of the Ku Klux Klan after the Reconstruction era, we're seeing a "peak moment" in racist backlash to the first black president. (Gillian Brockell,Kate Woodsome,Jesse Mesner-Hage/The Washington Post) 
 
 The United States defeated two murderous ideologies in the 20th century. So we should all be repulsed by the sight of our fellow Americans carrying the banners of either movement, whether they are waving the red flags of communism or black flags of Nazism. Yet we are not. Communism is not viewed as an evil comparable to Nazism today. As Alex Griswold recently pointed out, the New York Times has published no fewer than six opinion pieces this year defending communism, including essays praising Lenin as a conservationist, explaining why Stalinism inspired Americans, and arguing that the Bolsheviks were romantics at heart and that women had better sex under communism. Can one imagine the Times running similar pieces about the Nazis? 
 
 My mother and grandfather fought the Nazis in Poland during World War II, and her family then endured the Stalinist terror that followed, when Nazi occupation was replaced by Soviet domination. So forgive me if I see little moral distinction between the swastika and the hammer and sickle. Both are evil, and their modern adherents need to be condemned — especially when they dare to commit acts of violence in our midst to advance their hateful visions. 
 
 Both the left and the right have a responsibility to police their own movements. In the 1960s, William F. Buckley excommunicated the John Birch Society, widely believed then to be anti-Semitic and a proponent of nutty conspiracy theories, from the respectable right, and today, conservatives have a responsibility to do the same with the white nationalists of the alt-right. 
 
 Those on the left have responsibilities as well — responsibilities few are meeting. On Monday I asked the office of House Minority Leader Nancy Pelosi (D-Calif.) for her statement of condemnation. To her credit, Pelosi issued a strong statement Tuesday, declaring, “The violent actions of people calling themselves antifa in Berkeley this weekend deserve unequivocal condemnation, and the perpetrators should be arrested and prosecuted. In California, as across all of our great nation, we have deep reverence for the Constitutional right to peaceful dissent and free speech. Non-violence is fundamental to that right.” 
 
 Good for her. So why haven’t more leading Democrats done the same? After Charlottesville, the media rightly demanded that President Trump and all Republicans condemn the neo-Nazis and the KKK. So where are the calls for Democrats to condemn antifa — and the brutal public condemnation for those who fail to do so? If black-clad neo-Nazis had attacked peaceful protesters at a “No to Racism in America” march in Berkeley, politicians in Washington would be falling over themselves to express their disgust — and any who failed to do so would be vilified. But when neo-communists commit this kind of violence, they get a pass from the left. 
 
 That cannot be allowed to stand. 
 
 Read more from Marc Thiessen’s archive, follow him on Twitter or subscribe to his updates on Facebook.
– Sunday's violence in Berkeley has brought renewed attention to the "antifa" movement, general shorthand for groups of black-clad "anti-fascist" protesters who show up at rallies to confront far-right protesters. In his post-Charlottesville remarks, President Trump blamed the antifa movement for contributing to the violence, and Sunday's confrontation "marked another street brawl between opposing ends of the political spectrum—violence that has become a regular feature of the Trump years and gives signs of spiraling upward," per the Washington Post. So just what is antifa? In a New York Times op-ed, Columbia professor Todd Gitlin offers some insights, describing antifa as the "backlash to the backlash, a defensive response to the growing presence of right-wing extremism." Given antifa members' willingness to use violence, he sees cause for concern. "They do not advocate a positive doctrine, racial or otherwise," writes Gitlin of antifa adherents. "Some supporters consider themselves (as Mr. Trump accurately said) anarchists, some Marxists of different stripes." No national organization exists, and groups (usually all men) spring up locally. Antifa groups typically are unarmed, but Gitlin sees the potential for that to change as confrontations with right-wing groups escalate. "If effectively contained and self-contained, many of its supporters would likely return to the kind of nonviolent left-wing, anti-racist organizing that they were involved in before Mr. Trump rejuvenated the nationalist right with fire and fury," writes Gitlin. But that's not likely in the near future, he adds. "More Charlottesvilles, or worse, may be coming." Click for the full column.