The US House committee investigating the January 6, 2021, attack on the Capitol claimed that a tweet by former president Donald Trump in 2020 inspired far-right groups to take weapons to Washington to stop the certification of Joe Biden's 2020 presidential election victory.
“This tweet served as a call to action and in some cases a call to arms,” said panel member Stephanie Murphy, US Representative from Florida.
Some members face seditious conspiracy charges for their role in the assault on the Capitol.
"The president got everybody riled up, told everybody to head on down," testified rioter Stephen Ayres, who pleaded guilty to unlawfully entering the Capitol.
"So basically we were just following what he said."
Here is a look at the two extremist groups that the January 6 committee claims answered Mr Trump's plea to halt Mr Biden's certification.
Who are the Oath Keepers?
Founded in 2009, The Oath Keepers are a right-wing political organisation with ties to the militia movement.
The organisation's name comes from its core tenet — that members must uphold the oath they took as military personnel or law enforcement.
The Oath Keepers actively recruit members of the military, police and other law-enforcement officials.
The group sees "leftist groups, the deep state and supposed foreign conspirators or global cabals" as the most dangerous threat to American values, ABC News reported.
In a since-deleted blog post, the Oath Keepers follow a list of 10 "orders we will not obey" on unrealised threats from the government.
They include forcing citizens into concentration camps, imposing martial law or conducting military-style tribunals, the Centre for Strategic and International Studies reported.
Who is Jason Van Tatenhove?
Jason Van Tatenhove, a former spokesman for the group, told the January 6 committee that the Oath Keepers use violence, intimidation and propaganda as tools of persuasion.
The Oath Keepers were founded by Stewart Rhodes, who is in prison awaiting a trial on charges related to the assault.
Mr Van Tatenhove described the Oath Keepers as a "dangerous militia that is in large part fed by the ego and drive of" Mr Rhodes.
Mr Rhodes and 10 other Oath Keepers have been charged with seditious conspiracy.
Designated a terrorist entity by Canada and New Zealand, the Proud Boys are an extremist group known for their violent clashes.
The group gained notoriety during a 2020 debate when then-president Donald Trump told them to "stand back and stand by" when a moderator asked him to condemn them.
The group claims to abide by a list of libertarian principles but is most known for being Islamophobic, anti-Semitic, nationalistic and misogynistic, the Southern Poverty Law Centre said.
The Proud Boys have appeared in extremist rallies such as the "Unite the Right" 2019 rally in Charlottesville, Virginia.
Describing themselves as "western chauvinists", Proud Boys are distinguishable by their black-and-yellow Fred Perry polo shirts. The clothing company announced in 2020 it was withdrawing the shirt from the market.
Gavin McInnes, the group's founder, said its name comes from a song from the Disney film Aladdin.
There are four degrees of membership within the Proud Boys, the first being that they must declare that they are a "western chauvinist".
Proud Boys leader Enrique Tarrio is one of the most high-profile of the hundreds to have been charged since the 2021 attack on the Capitol.
Although he did not attend the riot that day, he allegedly claimed credit on social media and in an encrypted chat room.