Violence broke out in several locations in DC following a 'Stop the Steal' rally in support of Mr Trump's repeated and baseless allegations of electoral fraud.
Thousands of Trump loyalists marched downtown on Saturday afternoon to falsely claim that president-elect, Joe Biden, stole the 2020 presidential election.
Tensions began to boil over as darkness fell, with fistfights and brawling breaking out in several streets across the capital.
Video and images of the clashes show members of the far-right group, Proud Boys, clash with left-wing Antifa activists late into the night.
Four people were taken to hospital with stab wounds, DC fire spokesman, Doug Buchanan, said.
Their injuries were described as serious but not life-threatening. Authorities said 23 people had been arrested.
Meanwhile, law enforcement declared a riot in Olympia, Washington state, where one person was shot. The suspect was detained, Washington State Patrol said.
The condition of the shooting victim was not immediately clear. Four arrests were made in total and four officers injured, the force added.
The violence erupted just a day after the outgoing president suffered a Supreme Court defeat which further dents his desperate bid to hold onto the White House.
Justices on Friday rejected a lawsuit by the state of Texas which asked them to throw out election results in four key battleground states where Mr Trump lost to Mr Biden.
Protests broke out in several state capitals following the ruling.
The gatherings of mostly unmasked Trump loyalists were intended as a show of force just two days before the electoral college meets to formally elect Mr Biden as the 46th president.
Mr Trump, whose term ends on 20 January refuses to concede while clinging to baseless claims of voter fraud.
The defeated incumbent tweeted his apparent surprise on Saturday morning at the rallies, publicly known for weeks: “Wow! Thousands of people forming in Washington (D.C.) for Stop the Steal. Didn’t know about this, but I’ll be seeing them! #MAGA".
He left the White House around midday for the trip to the Army-Navy football game at the US Military Academy in West Point, New York. As the Marine One helicopter passed over a rally on the National Mall, cheers went up.
Michael Flynn the former national security adviser recently pardoned by Mr Trump was speaking from the stage at the time.
“That’s pretty cool. Imagine just being able to jump in a helicopter and just go for a joy ride around Washington,” said Mr Flynn, whose pardon wiped away his conviction for lying to the FBI on two occasions during the Russia investigation.
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