WASHINGTON - Prosecutors in the trial of five Oath Keepers members on Friday showed a jury fresh evidence that the right-wing militia group's founder Stewart Rhodes told his followers ahead of last year's U.S. Capitol attack there would be a "bloody" war if then-President Donald Trump failed to reverse his 2020 election loss.

In numerous text messages, online postings and speeches shown as evidence, Rhodes promoted the use of force and implored Trump to invoke the Insurrection Act, a 19th century U.S. law that empowers presidents to deploy troops to quell civil unrest.

Trump never invoked the Insurrection Act even as Rhodes wrote to him in open letters posted online about the idea and bragged to fellow Oath Keeper leaders in a December 2020 text that he was "on back-channel working groups trying to advise the president."

Rhodes and his four co-defendants are on trial on felony charges including seditious conspiracy. A second set of Oath Keeper defendants accused of being part of the same conspiracy are slated to go to trial in November.

"Show the world who the traitors are, and then use the ... Insurrection Act to drop the hammer on them," Rhodes was seen saying in a December 2020 speech at a pro-Trump political rally in video presented to the jury. "If he does not do it now, while he is commander in chief, we are going to have to do it ourselves later, in a much more desperate, much more bloody war."

Rhodes and his four co-defendants - Thomas Caldwell, Kenneth Harrelson, Kelly Meggs and Jessica Watkins - are on trial on charges accusing them of conspiring to prevent Congress from certifying Democrat Joe Biden's election victory on Jan. 6, 2021, in a bid to keep the Republican incumbent in power. A pro-Trump mob stormed the Capitol on that day and attacked police, but failed to prevent the election certification.

Seditious conspiracy is a rarely prosecuted crime under a statute dating to the 19th century Civil War era, defined as attempting "to overthrow, put down or to destroy by force the government of the United States." It carries a possible prison sentence of 20 years.

A member of another far-right group, the Proud Boys, on Thursday pleaded guilty to seditious conspiracy for his role in the Capitol attack. Three Oath Keepers members this year pleaded guilty to seditious conspiracy, and may be called as witnesses in the current trial.

Testifying on Friday were Capitol Police Special Agent Ryan McCanley and FBI Special Agent Byron Cody, both answering questions about the material that the government introduced as evidence. Friday marked the fourth day of testimony from prosecution witnesses, with the trial set to resume on Tuesday with Cody returning to the witness stand.

Prosecutors have said some of the Oath Keepers were among the Trump supporters who stormed the Capitol building after he gave a speech to supporters repeating his false claims that the election had been stolen from him through widespread voting fraud. Five people died during and shortly after the riot and about 140 police officers were injured.

In addition, prosecutors have said the Oath Keepers organized a "quick reaction force" of armed members who were kept on standby across the Potomac River in Virginia in case they were called upon to bring firearms into Washington.

Attorneys for the defendants have said the evidence will show they did nothing illegal and that the Oath Keepers are a peacekeeping group that has done security work at events around the country to protect speakers at political rallies.

Various text messages, Facebook direct messages and audio recordings used as evidence in the trial have shown the defendants vowing to reject Biden's election victory, planning to go to Washington and discussing what weapons they could bring, with Rhodes talking of possible "civil war."

Prosecutors and defense attorneys are expected next week to address a dispute over whether the government can introduce potentially incriminating communications between Rhodes and Kellye SoRelle, the Oath Keepers' general counsel who is facing related criminal charges in a different case.

In one text, briefly posted before the defense objected, Rhodes told SoRelle: "They won't fear us till we come with rifles in hand."

(Reporting by Sarah N. Lynch and Chris Gallagher; Editing by Will Dunham, Scott Malone and Deepa Babington)