The day President Trump’s supporters stormed the Capitol, Jeremy Michael Brown, a retired Special Forces soldier with multiple combat tours, was in Washington, D.C., dressed for battle in body armor, boots and a Kevlar helmet.

Brown who had spent months warning the United States was on the verge of tyranny and “total war,” said in a brief interview that he had gone to the nation’s capital to “provide security” at the rally.

There’s no evidence to suggest that Brown, 46, a former master sergeant, entered the Capitol building with rioters, and he has not been charged with any crime. But the killing of a fellow Air Force veteran by police inside the Capitol left Brown enraged at the very government he had over the course of a long military career sworn an oath to defend and serve.

“Wanna shoot an UNARMED VETERAN attempting to UPHOLD her Oath? The SAME oath you F---ING COWARDS seem to forget YOU took YOURSELF!” he wrote in a post on Parler, a social media site increasingly under scrutiny for an abundance of threatening messages. He challenged the Capitol Police to a “duel” and posted a video of the moment Ashli Babbitt was killed.

“WHAT ELSE DO YOU F---ING NEED!” he exhorted his followers on Parler. “WATCH!!! THEN CHOOSE! JOIN or DIE!”

A Washington Post analysis of individuals who breached the Capitol or were in the vicinity of the riots identified 21 people with some prior military service background. Of the 72 arrested or charged by state and federal authorities through Thursday morning, 11 have military backgrounds.

The military personnel and veterans involved in the demonstrations and riot at the Capitol range in age from 33 to 62. A handful of the veterans served in combat or with front-line infantry units in the Army and Marine Corps and spoke regularly of a coming revolution or the need for violent action to purge their country of unspecified enemies. Other veterans at the Capitol on Jan. 6 served for only short stints in the military or were focused more on clerical tasks than preparing for combat. Like many at the riots, they were swept up in conspiracy theories that have taken hold among some of Trump’s most fervent supporters and felt called to action by the president’s repeated insistence without evidence that the election had been stolen.

The Pentagon hasn’t said how many active-duty troops or reservists are under investigation for any role in the protest or the riots, but homegrown militants and white supremacist groups have long targeted veterans for recruitment.

And some analysts who track extremist groups warn that the military has been slow to recognize the problem.

“They are behind in having the capacity to investigate these issues,” said Michael Edison Hayden, a spokesman for the Southern Poverty Law Center, which tracks hate groups. “They don’t have the proper tools to identify symbols and tattoos and that kind of thing, so it has allowed it to fester for a really long time.”

In an extraordinary sign of concern, the Pentagon’s top generals emphasized this week in a letter to the force that “the U.S. military will obey lawful orders from civilian leadership” and cautioned that “the rights of freedom of speech and assembly do not give anyone the right to resort to violence, sedition and insurrection.”

National security analysts warned that veterans could be particularly susceptible to recruitment by right-wing extremist groups, especially when their messages seem to be in sync with those of the president, who has railed against alleged deep-state actors seeking to rob him of his authority and rig the 2020 election.

“The president has created a permission structure [for troops and veterans],” said Katrina Mulligan, the managing director for national security and international policy at the Center for American Progress. “They believe that they are doing what he wants them to do. . . . He’s the commander in chief; the person they’ve been taught more than any other person is the ultimate authority.”

Extremist groups also play on veterans’ desire to serve a larger cause and leverage the disappointment many feel in a society that constantly tells them that they are special and unique but doesn’t always treat them that way.

“There’s this need among veterans to be recognized and be part of a solution to something big,” said Jason Dempsey, an Afghanistan war veteran and adjunct senior fellow at the Center for a New American Security. “They want to be seen as patriots and are searching for immediate gratification.”

The desire to be seen as superpatriots defending the country from internal threats is a recurrent theme in the statements and social media posts of veterans arrested in the riots.

Jacob Fracker, 29, and Sgt. Thomas “T.J.” Robertson, 47, served in the Army and Marine Corps, fought overseas and came home to jobs as police officers in Rocky Mount, Va. The two men posed for a selfie inside the Capitol in front of a statue of John Stark, a Revolutionary War hero.

In one comment included as evidence in the criminal complaint against him, Robertson wrote that he was “PROUD” of the photo. “If you are too much of a coward to risk arrest, being fired, and actual gunfire to secure your rights, you have no words to speak [that] I value,” he wrote, according to the complaint.

After his arrest he defended his actions as consistent with his military oath. “I am a veteran of Iraq and Afghanistan where I was wounded severely,” he added in a statement that he shared with a Roanoke television station. “I fought and bled for the rights of all Americans.”

Larry R. Brock, a retired Air Force lieutenant colonel, who was photographed carrying zip-tie handcuffs on the Senate floor, similarly described himself online as a patriot and savior. Brock, a former A-10 pilot who said he deployed to Iraq and Afghanistan, was fired two years ago from his job with an aviation training company for threatening to shoot “members of a particular religion and/or race,” according to a 2018 letter of termination submitted by authorities in his case.

A week before he stormed the Capitol, he wrote on Facebook that he saw no distinction among the Democrats, the Biden administration and “an invading force of Chinese communists.”

He signed off on the post: “Against all enemies foreign and domestic,” a reference to the oath he took as a military officer. He also included hashtags singling out the Oath Keepers and Three Percenters, far-right groups that are known to recruit veterans and police.

Other veterans caught up in the rioting in the Capitol seemed to have fallen prey to the same delusional conspiracy theories that have gripped their civilian counterparts. Jacob Anthony Chansley, who served two years in the Navy as a low-ranking sailor, paraded through the Capitol wearing a fur headdress with horns and a spear. Chansley, who calls himself Q-Shaman, is a fervent believer in QAnon, the conspiracy theory that alleges Trump is fighting to save the United States from a cabal of pedophiles.

Still other veterans arrested in the Capitol riots seemed most interested in garnering attention. Nick Ochs, a former Marine, member of the Proud Boys right-wing group and aspiring right-wing troll, posted a photo of himself smoking a cigarette inside the Capitol during the riots. After the melee, he joked in a video that he was “being sarcastic” when he said he had come to Washington to stop the certification of President-elect Joe Biden’s election and expressed delight that his antics, and the violence that left five dead, had caused Congress to pause its work.

Among the chilling questions from last week’s riot is how many veterans with combat training are committed to using their skills in defense of their delusional beliefs. Even before the Capitol riots, Brown, who Army officials said deployed twice each to Iraq and Afghanistan, sought to recruit his fellow Green Berets on Twitter to join a group he was trying to form in Texas.

“We CANNOT rely on Politicians and to Tyrants. That is like asking a child to stop the Ice Cream from selling Ice Cream,” he wrote in May on Twitter. “There’s but one weapon against Tyranny & that is the PATRIOT!!! Start mobilizing your neighborhoods. America is under attack!”

Paul Sonne and Jennifer Jenkins contributed to this report.