Former Proud Boys leader Enrique Tarrio and four lieutenants charged with seditious conspiracy in the Capitol attack “took aim at the heart of our democracy” on Jan. 6, 2021, a federal prosecutor told jurors on Thursday as their high-profile trial opened in Washington.

Jurors began hearing attorneys’ opening statements more than two years after members of the far-right extremist group joined a pro-Donald Trump mob in attacking the Capitol.

Assistant U.S. Attorney Jason McCullough said the Proud Boys knew that the prospects of a second term in office for Trump were quickly fading as Jan. 6 approached. So the group leaders assembled a “fighting force” to stop the transfer of power to Joe Biden, McCullough said. Tarrio saw a Biden presidency as a “threat to the Proud Boys’ existence,” the prosecutor said.

“These men did not stand back. They did not stand by. Instead, they mobilized,” McCullough told jurors, invoking the words of Trump when he infamously told the Proud Boys to “stand back and stand by” during a 2020 presidential debate with Biden.

The trial comes on the heels of the seditious conspiracy convictions of two leaders of the Oath Keepers, another far-right extremist group. Several other Oath Keepers members were charged with plotting to stop the peaceful transfer of presidential power from Trump, a Republican, to Biden, a Democrat.

The case against Tarrio and his four associates is one of the most consequential to emerge from the Jan. 6 riot at the Capitol. The trial will provide an in-depth look at a group that has become an influential force in mainstream Republican politics.

Defense lawyers have said there was never any plan to go into the Capitol or stop Congress’ certification of the electoral vote won by Biden. And they have accused prosecutors of trying to silence potential defense witnesses. Tarrio’s lawyers have not said whether he will take the stand in his defense.

Tarrio’s co-defendants are Ethan Nordean, of Auburn, Washington, who was a Proud Boys chapter president; Joseph Biggs, of Ormond Beach, Florida, a self-described Proud Boys organizer; Zachary Rehl, who was president of the Proud Boys chapter in Philadelphia; and Dominic Pezzola, a Proud Boy member from Rochester, New York.

The Justice Department has charged nearly 1,000 people across the United States over the deadly Jan. 6 insurrection, and its investigation continues to grow.

The Proud Boys’ trial is the first major trial to begin since the House committee investigating the insurrection urged the department to bring criminal charges against Trump and associates who were behind his efforts to overturn his 2020 election loss.

While the criminal referral has no real legal standing, it adds to political pressure already on Attorney General Merrick Garland and the special counsel he appointed, Jack Smith, who’s conducting an investigation into Jan. 6 and Trump’s actions.

Jury selection in the case took two weeks as a slew of potential jurors said they associated the Proud Boys with hate groups or white nationalism. The Capitol can be seen in the distance from parts of the courthouse, where a second group of Oath Keepers are also currently on trial for seditious conspiracy, which carries up to 20 years behind bars upon conviction.

Tensions bubbled over at times as jury selection slowed to a crawl and defense lawyers complained that too many potential jurors were biased against the Proud Boys. Defense attorneys challenged jurors who expressed support for causes such as Black Lives Matter, saying that could indicate prejudice against the Proud Boys.

Lawyers and the judge clashed during sometimes chaotic pretrial legal wrangling to the point where two defense attorneys threatened to withdraw from the case. U.S. District Judge Timothy Kelly, a Trump appointee, lashed out after defense lawyers repeatedly interrupted and talked over him on Wednesday, warning that he would find them in contempt if it continued.

Tarrio, who’s from Miami, wasn’t in Washington on Jan. 6 because he was arrested two days before the riot and charged with vandalizing a Black Lives Matter banner at a historic Black church during a protest in December 2020. He was ordered to leave the capital, but prosecutors say he remained engaged in the extremist group’s planning for Jan. 6.

Prosecutors are expected to tell jurors that as the Proud Boys’ anger over the election grew, they also began to turn against police over Tarrio’s arrest and over the failure to bring charges in the stabbing of another Proud Boy during clashes the month before the riot.

Communications cited in court papers show the Proud Boys discussing storming the Capitol in the days before the riot. On Jan. 3, someone suggested in a group chat that the “main operating theater” be in front of the Capitol. “I didn’t hear this voice note until now, you want to storm the Capitol,” Tarrio said the next day in the same chat.

Tarrio’s lieutenants were part of the first wave of rioters to push onto Capitol grounds and charge past police barricades toward the building, according to prosecutors. Pezzola used a riot shield he stole from a Capitol Police officer to break a window, allowing the first rioters to enter the building, prosecutors allege.

Prosecutors say Tarrio cheered on the actions of the Proud Boys on the ground as he watched from afar.

“Do what must be done. #WeThePeople.” he wrote on social media as the riot unfolded. “Don’t (expletive) leave,” Tarrio wrote in another post.