Organizers said "at least 8 million people gathered today at more than 3,300 events across all 50 states," from big cities and small towns. US authorities provided no national crowd estimate.

It was the third time in less than a year that Americans have taken to the streets as part of a grassroots movement called "No Kings," the most vocal and visual conduit for opposition to Trump since he began his second term in January 2025.

In New York, America's most populous city, tens of thousands of demonstrators rallied, including Oscar-winning actor Robert De Niro, a frequent Trump critic, who called the president "an existential threat to our freedoms and security."

Protests unfolded from Atlanta to San Diego, with Alaskans joining the mix later in the day.

"No country can govern without the consent of the people," 36-year-old military veteran Marc McCaughey told AFP in Atlanta, where thousands turned out.

"We're out here because we feel that the Constitution is under threat in a multitude of different ways. Things aren't normal. They aren't okay."

In the Michigan town of West Bloomfield, near Detroit, people braved below-freezing temperatures to protest.

And in the US capital Washington, thousands of marchers -- some carrying banners that blared "Trump Must Go Now!" and "Fight Fascism" -- flocked to the National Mall.

"He keeps lying and lying and lying and lying, and no one says anything. So it's a terrible situation we're in," 67-year-old retiree Robert Pavosevich told AFP.

Trump himself was in Florida for the weekend.

In Minnesota, a flashpoint in Trump's crackdown on illegal immigration, a massive rally was held outside the state capitol in Saint Paul. Many held aloft posters bearing photos of Renee Good and Alex Pretti, US citizens fatally shot by federal immigration officers in Minneapolis this year. 

Minnesota Governor Tim Walz, the Democratic vice presidential nominee in 2024, told the crowd that their resistance to Trump and his policies makes them "the heart and soul" of everything good about the US. 

"They call us radicals," Walz said. "You're damn right we've been radicalized - radicalized by compassion, radicalized by decency, radicalized by due process, radicalized by democracy, and radicalized to do all we can to oppose authoritarianism."

US Senator Bernie Sanders of Vermont, a Trump critic who sought the Democratic presidential nomination in 2016 and 2020, also addressed the event in Minnesota. Musician Bruce Springsteen performed his song "Streets of Minneapolis" - a ballad criticizing Trump's immigration crackdown and lamenting the deaths of Good and Pretti.

"We will not allow this country to descend into authoritarianism or oligarchy in America," said Sanders, an independent. "We, the people, will rule."

The National Republican Congressional Committee criticized Democratic politicians and candidates for supporting the rallies.

"These Hate America Rallies are where the far-left's most violent, deranged fantasies get a microphone and House Democrats get their marching orders," committee spokesperson Mike Marinella said in a statement.

In New York, a crowd that police estimated at tens of thousands stretched more than 10 blocks in midtown Manhattan. Actor Robert De Niro, one of the organizers, said that no president before Trump has posed "such an existential threat to our freedoms and security."

Holly Bemiss, 54, said she and other New York rally attendees were acting in the same spirit as her ancestors who fought in the American Revolution. 

"We fought against having kings and we fought for freedom," she said. "We're just doing it again."

The anti-Trump mood has spilled beyond US borders, with rallies Saturday in European cities including Amsterdam, Madrid and Rome, where 20,000 people marched under a heavy police presence.