Thousands of Donald Trump supporters alleging electoral fraud converged on several US cities and towns on Saturday and there were isolated scuffles with counter-demonstrators.
In Washington DC, more than 20 people were arrested and four people were stabbed, police said.
Mr Trump lost the 3 November election to Joe Biden but is yet to concede.
The Electoral College, the system which elects US presidents, is due to endorse Mr Biden’s victory on Monday.
Mr Biden won 306 votes to Mr Trump’s 232 in the Electoral College, and gained over seven million more votes than his Republican rival in the popular vote.
In the nation’s capital, police sought to keep the two sides apart, a strategy that included sealing off Black Lives Matter Plaza where counter-demonstrators had gathered.
Pro-Trump demonstrators, rallying under the banner of “Stop the Steal”, were joined by members of the far-right Proud Boys, dressed in yellow and black, many wearing bullet-proof vests.
Mr Trump caused controversy by saying the group should “stand back and stand by” during a September presidential debate, though he later condemned “all white supremacists”.
As night fell, Proud Boys and antifa counter-demonstrators, mostly separated by police lines, yelled insults at each other. But sporadic violence broke out.
Rallies also took place in Olympia, the capital of Washington state, Atlanta and St Paul, Minnesota. Police in Olympia said one person had been shot and three arrested as rival groups clashed.
The Washington DC rally attracted several thousand Trump-supporters but it was smaller than a similar event on 14 November. Few participants wore masks despite Covid-19 restrictions.
There were speeches by Mr Trump’s now pardoned former National Security Advisor, Michael Flynn, and Sebastian Gorka, another former White House official.
Mr Gorka urged the president not to give up his legal campaign – based on debunked allegations of electoral fraud – to reverse the election result.
The president’s latest legal defeat came on Friday when the Supreme Court rejected an unprecedented attempt to throw out results in four battleground states which Mr Biden won. Mr Trump has now lost more than 50 cases linked to the election.
Cheers erupted as the presidential helicopter, Marine One, flew over the Washington rally carrying Mr Trump to the Army-Navy football game at West Point, New York.
The president had earlier tweeted his support.
General Flynn likened the protesters to soldiers and priests breaching the walls of Jericho, echoing the rally organisers’ call for “Jericho Marches” to overturn the election result.