The event was largely peaceful, but grew violent after crowds thinned at night.
President-elect Joe Biden is moving forward with transition plans, capping a tumultuous and tension-filled campaign during a historic pandemic against President Donald Trump, who still refuses to concede the election one week after Biden was projected as the winner of the presidential race.
Trump has largely hunkered down inside the White House since the election, but on Saturday his motorcade drove drove past supporters gathered to rally in Washington, D.C., on his way to play golf.
Biden, meanwhile, is pressing forward, meeting with transition advisers in Delaware and calling Trump's refusal to concede "an embarrassment."
The Biden transition team and the Trump administration are in a standoff over whether Biden should be granted access to federal resources allocated for the transition of power. The General Services Administration, headed by a Trump appointee, has yet to officially recognize Biden as the victor in the election, preventing Biden's team from gaining full access to government funds and security information.
But a growing number of Republican senators are calling on the administration to start giving Biden classified intelligence briefings, a sign that support for Trump's refusal to concede the election may be waning among his allies on Capitol Hill.
Vice President Mike Pence and Second Lady Karen Pence will be at the Cape Canaveral Air Force Station Sunday to see the attempted launch of Crew-1 mission to the International Space Station, which is currently set for at around 7:27 p.m. eastern time.
At least 20 people were arrested as pro-Trump demonstrators and counterprotesters gathered in the nation's capital on Saturday.
The majority were arrested for minor incidents. However, late in the day, as the crowds thinned and the scene got more violent, police said one protester was stabbed multiple times. Seven guns were confiscated during the day's events as well, police said.
The Metropolitan Police Department did not release the charges for all 20 people, but said earlier in the day that four people were arrested for firearms violations, two were arrested for simple assault, two were arrested for disorderly conduct, one person was arrested for not having a permit and one was arrested for assault on a police officer.
Two police officers were also injured.
The Metropolitan Police Department announced the arrests just before 10 p.m., but said a full report of those arrested would be released on Sunday.
Police had warned those set to gather for the event that open carry of firearms is illegal in Washington, D.C. Authorities were hoping to stem the tradition of some so-called militia groups who have shown up to protests around the nation openly displaying weapons.
The large groups marching in Washington during the daylight hours were largely peaceful.
ABC News' Ben Siu and Will Gretsky contributed to this report.
A small crowd of Trump supporters have gathered outside the Trump National Golf Club in Virginia, according to a pool report.
About 30 supporters were on the sidewalk outside the club Saturday afternoon, waving flags and banners, the report said. One person had a handwritten "Stop the steal" sign."
Trump was seen arriving at the golf club earlier on Saturday, where he was met by protesters rallying against him.
One week after addressing the nation for the first time as president-elect from Wilmington, Delaware, Joe Biden has penned an open letter to his home state published by the Delaware News Journal, thanking its denizens for helping him get to the Oval Office after nearly 50 years in public life.
“This election was won by bringing Americans from all walks of life together. It was won because of the hard work and faith of so many people across this country. It was won with a promise to restore the soul of this nation and build back better than ever. However, we never could have done it without you -- without Delaware,” Biden wrote in the letter, which the publication said it asked him to write.
As he often did on the trail, Biden spoke about the values he learned growing up, and the president-elect offered the same unity pitch he delivered last week.
“Our country has never needed the values I learned here in Delaware more. That’s why, although I am a proud Democrat, I promise you, I will be an American President, and work as hard for those who didn’t vote for me, as those who did,” he said.
-ABC News' Molly Nagle
