In the two weeks that saw an uprising against racial injustice and police brutality spread from the streets of Minneapolis to cities across America, the specter of violent, left-wing militants invoked by President Trump and a chorus of conservative voices has yet to materialize.

Instead, multiracial crowds have appeared in every corner of the United States, as the president sent more than a dozen tweets blaming clashes with police on antifa, the label associated with anti-fascist protesters who infamously sparred with far-right figures after his election in 2016. He went so far as to say he would designate antifa as a “terrorist organization,” though he does not have the legal authority to apply that label to a domestic group.

The nation’s top law enforcement officials joined the president’s attacks. FBI Director Christopher A. Wray directed blame for violence tinging the protests over the killing of George Floyd at “anarchists like antifa and other agitators.” Attorney General William P. Barr claimed, but did not offer, “evidence that antifa and other similar extremist groups, as well as actors of a variety of different political persuasions, have been involved in instigating and participating in the violent activity.”

But the group the Trump administration has labeled a menace has mostly been nonexistent, experts and law enforcement officials say, and certainly has not been orchestrating what have been largely peaceful protests. Despite warnings of antifa incursions in scores of cities, there is no evidence linking outbursts of violence to an organized left-wing effort. And those associated with the autonomous groups that went up against far-right figureheads four years ago — and whose roots go back to earlier left-wing causes — say there is no such centralized organization.

Federal and local arrest records in dozens of cities make virtually no mention of antifa. Law enforcement officials who had braced for the purported invasion of antifa militants in cities large and small now mostly acknowledge the threat has not appeared.

The reason, according to local leaders familiar with antifa as well as activists who became its public face, is that the demonstrations in recent weeks bear little resemblance to earlier battles between right-wing extremists and left-wing militants. Those skirmishes reached a fever pitch with the deadly “Unite the Right” rally in Charlottesville, and also rattled cities from Washington to Berkeley, Calif.

Now, something bigger is underway, they say.

In the crowd of thousands recently filling the streets of Berkeley, many might align themselves against fascism, observed the city’s mayor, Jesse Arreguín. Meaning: They distrust centralized control in the hands of leaders who vilify outsiders and crush opposition.

As for antifa, the Democratic mayor has seen few traces of the black-clad militants he once condemned as a gang. “I don’t see them,” Arreguín said.

The absence of antifa from protests roiling Berkeley — a crucible of left-wing activism — is a sign, Arreguín said, of the scale and possible significance of the protests. They are not driven by left-wing zealots, he said, but by multiracial and multigenerational crowds seeking a reckoning with systemic problems of racism and policing.

“Anti-fascist protesters thought that because of the threat that white supremacists and fascists brought to their communities, particularly after the deadly events in Charlottesville in 2017, that they had to defend themselves,” Arreguín said. “This is very different. This is about something bigger.”

The difference was expressed another way by Yvette Felarca, a Berkeley middle school teacher charged in 2017 with felony assault for allegedly punching a man with a neo-Nazi flag. (The assault charge was later dropped.)

“Trump has turned everybody into antifascists,” Felarca said. “There’s no organization called ‘antifa.’ It was always just people prepared to take action against fascism. It turns out, that’s a lot of people.”

Some of those people have taken extreme measures in recent weeks, leading to arrests.

But no meaningful link to antifa has yet been established, law enforcement officials said, while cautioning that investigations were ongoing and there were possible signs of participation by extremists of various types.

Nationwide, officials have arrested more than 13,000 people in 39 U.S. cities since May 27, according to a Washington Post tally of data provided by police departments and included in media reports. In several cities that released the addresses of arrested individuals, the vast majority lived in the cities and towns closest to the protests. Thousands of protesters were arrested for curfew violations and other minor charges, such as obstructing a roadway or carrying an open container.

More serious federal charges, brought against individuals for offenses such as throwing molotov cocktails at police vehicles, reveal no evidence of a plot by antifa to create discord.

A complaint filed in U.S. District Court in Las Vegas accuses three men with alleged ties to the far-right “Boogaloo” movement, whose members anticipate civil war and civilizational collapse, of plotting to provoke violence at recent protests.

In the nation’s capital, police arrested 430 people connected to protests during the past two weeks. Charges ranged from burglary to rioting. But prosecutors have not seen “any indication” of involvement by “an extremist, left-wing group like antifa,” said Karl A. Racine, the District’s attorney general.

The same is true in other places where the unrest has been most acute. Antifa has not been identified as a meaningful player in Minneapolis, where the protests began last month, according to a federal law enforcement official who spoke on the condition of anonymity because they were not authorized to discuss ongoing intelligence gathering.

Antifa has similarly not been tied to events in Seattle, where protesters marched on city hall and occupied the streets adjacent to a police precinct.

Late Wednesday, Trump threatened to take over Seattle after some of the Internet’s most prominent right-wing personalities spent the day blaming antifa for the upheaval.

Their claims were contradicted by local law enforcement.

“We have no evidence that antifa are in any way involved in the ongoing protests,” said Patrick Michaud, a Seattle police spokesman.

Instead, the purported peril of antifa rests on what the Atlantic Council’s Digital Forensic Research Lab characterized this week as a “disinformation campaign, in which far-right activists have spread fears of antifa ‘terrorism’ by way of largely spurious, decontextualized or provably false claims.”

From Evansville, Ind., to Snohomish, Wash., rumors and disinformation about the impending antifa push into small-town America — in some cases warning of busloads of outsiders ready to storm tranquil communities — have not just duped unsuspecting residents, but forced local law enforcement to mobilize in response.

Billy Bolin, the Evansville police chief, wrote on his personal Facebook page in response to rumors of outside infiltration that his department was “planning for numerous scenarios,” adding, “My philosophy is plan for the worst and hope for the best.”

Keith Rogers, the chief of police in Snohomish, a city of 10,000 residents near Seattle, was reassigned this week over his handling of an armed counterprotest fueled by false online warnings about antifa. He initiated an “emergency response operation” involving the fire department, county sheriff’s office, the mayor and the city administrator, as he told a recent meeting of the city council.

“The FBI and the Department of Homeland Security formally classifies antifa as a violent domestic terrorist group,” he falsely told the body. A Republican state lawmaker, Robert Sutherland, boasted on Facebook of “defending my little town of Snohomish from rioting and looting by antifa thugs.” It never occurred.

Among the only charges explicitly mentioning antifa emerged from protests in Austin, where authorities in Travis County say three people, all in their 20s, who looted a Target have ties to a now-defunct activist collective called the Austin Red Guards.

Arrest warrants filed this week describe the organization as a “self-identified communist/socialist antifa group” but include few additional details. There was no response to a message sent to the Red Guards over Facebook, where a post in December 2018 announced, “This project has reached its conclusion, we are no more.”

In San Antonio, a 43-year-old man was recently arrested on charges of terrorist threats and public fear for promising on Twitter to “personally kill” any “antifa soldiers” preparing to join a local protest.

In Columbus, Ohio, a school bus operated by circus performers was stopped by police, who said there was “a suspicion of supplying riot equipment to rioters” in a tweet that reached Sen. Marco Rubio (R-Fla.), the acting chairman of the Senate Intelligence Committee, who has warned repeatedly about signs of antifa. A spokesman for the senator did not respond to requests for comment about what these signs were.

“I don’t think there is an antifa,” said Todd Shanker, a federal defender involved in one of the most recent cases in which federal prosecutors accused a defendant of having ties to antifa. His client pleaded guilty last year to a misdemeanor for spray-painting crude language about U.S. Immigration and Customs Enforcement on a Detroit office building, following what the government called an “antifa protest.”

That police and local leaders are ensnared by the online rumors of antifa’s presence — which ricochet around social media but unravel on closer investigation — helps buttress the president’s efforts to point to far-left instigators.

Trump’s suggestion on Tuesday that a 75-year-old peace activist knocked to the ground by police in Buffalo was an “antifa provocateur” marked the latest escalation in an apparent attempt to discredit all dissent, said Mark Bray, a historian at Rutgers University and the author of “Antifa: The Anti-Fascist Handbook.”

“If you were to play it out, if there were this conspiratorial outfit that burned down much of the country, it would be a huge issue, requiring a major response,” Bray said. “But we haven’t seen that, other than some tweets, and that’s because it’s political theater.”

Antifa no longer exists, at least not in the form in which it has featured on the president’s Twitter feed or propaganda outlets, including the state-backed Russian channel RT, said Adam Klein, a professor of communication studies at Pace University who has analyzed antifa’s confrontation with white supremacists in Charlottesville in 2017.

“I’m sure there are people on the streets today who see themselves as anti-fascist,” Klein said. “But any kind of broader organization has been pretty dormant.”

On the most active antifa accounts on social media, Klein said, there is commentary about recent protests and occasional attempts to unmask far-right actors, but there have been “no calls for destruction or fighting police.”

According to the Atlantic Council’s analysis, the first noteworthy Twitter mention seeking to tie antifa to recent protests was from a popular account devoted to the QAnon conspiracy theory. It asserted on May 27 that the demonstrations were being engineered by financier George Soros, who looms large in anti-Semitic theorizing about a “Deep State” cabal.

Assertions about antifa have been issued from the depths of Twitter but also from the heights of U.S. law enforcement. Kerri Kupec, a Justice Department spokeswoman, said Barr’s remarks pointing to antifa were based on “information given to us by federal, state and local authorities,” but she declined to say more about the information.

“We have some investigations underway and very focused investigations on certain individuals that relate to antifa,” the attorney general said in a Fox News interview this week.

The refusal to offer evidence drew a rebuke this week from Senate Democrats, who sent a letter on Tuesday to Wray and to John Ratcliffe, the director of national intelligence. A spokeswoman for the FBI acknowledged receipt of the letter but declined to comment beyond pointing to Wray’s earlier remarks.

“These claims are highly inflammatory,” wrote Senate Minority Leader Charles E. Schumer (N.Y.), along with the top Democrats on the Senate Intelligence Committee, Sens. Mark R. Warner of Virginia and Dianne Feinstein of California. “They also appear intended to frame the legitimate peaceful protests taking place around the country as terrorist threats in order to justify unnecessary federal, even military, intervention and the excessive use of force.”

“These actions are not sustainable in a democracy,” the lawmakers wrote.

Keith L. Alexander, Alice Crites, Meryl Kornfield, Jenn Abelson, Nicole Dungca, Austin R. Ramsey, Jacob Wallace, Verónica Del Valle and Christopher Casey contributed to this report.