WASHINGTON — Just before they went to hear President Donald J. Trump speak on the day of the Capitol riot last year, Rocky Hardie, at the time a member of a Texas militia, and a friend, Guy Wesley Reffitt, made their preparations, Mr. Hardie testified in federal court on Friday.

They strapped pistols to their bodies, he said, and left assault rifles in the back of their car just in case “something bad happened” and they “needed to get them quickly.”

Mr. Hardie never went into the Capitol that day, but his account helped bolster the government’s claims that Mr. Reffitt, the first defendant in a Jan. 6 prosecution to face trial, had been at the leading edge of an advance on the police outside the building.

While the two men lost each other in the crowd, they met up later at their hotel, Mr. Hardie said, where Mr. Reffitt, showing off his injuries, bragged about walking through a barrage of pepper balls and urging the mob around him to push forward.

The account by Mr. Hardie, a onetime member of the Texas Three Percenters militia group, came on the fifth day of Mr. Reffitt’s trial — the first of more than 700 cases related to the Capitol attack to reach a courtroom. On Thursday, in an unusually emotional appearance, Mr. Reffitt’s teenage son testified against him, saying he had turned his father in to the F.B.I.

Mr. Reffitt has been charged with five counts related to the riot, including obstructing the work of Congress on Jan. 6, 2021, when a joint session of the House and the Senate met to certify the results of the 2020 election.

At the end of the day on Friday, Mr. Reffitt’s lawyer, William Welch, said it was unlikely that he would call any witnesses in defense of his client. Judge Dabney L. Friedrich, who is presiding over the trial, said the case could go to the jury early next week.

A balding and bespectacled man who runs a business making “in-ear earphones,” as he called them, Mr. Hardie, who has since left the militia group, was testifying under an immunity deal with the government. In his two hours on the stand, he gave the jury insight into the arcane world of right-wing militias and traced the arc of his relationship with Mr. Reffitt from early meetings of the Three Percenters to their 2,000-mile road trip to Washington last year.

The two men, both from Texas, met in the summer of 2020, amid a spate of racial justice protests — at a time, as Mr. Hardie put it, when “YouTube was full of people rioting and burning and firebombing.” Both had joined the Texas Three Percenters, a state group affiliated with a nationwide far-right movement that takes its name from the supposed 3 percent of the U.S. colonial population that fought against the British.

Mr. Reffitt struck Mr. Hardie as a can-do sort of guy, and one day they got together in a local park to discuss politics and their mutual loathing of Congress. Both agreed that Speaker Nancy Pelosi was “evil incarnate” and that most Washington politicians were “corrupt and destroying the country,” Mr. Hardie said.

Their concern about the nation deepened after the election — “a catastrophic event,” as Mr. Hardie called it, which they believed had been marred by fraud and cheating. By then, a group chat shared by the Texas Three Percenters was marked by “an apocalyptic tone,” he said, as several members discussed the vote results and eventually a plan to go to Washington in January.

Mr. Hardie and Mr. Reffitt decided to go together, and after packing radios, body armor, two pistols and a pair of AR-15 rifles into the back of a Chevrolet Equinox owned by Mr. Reffitt’s wife, they left for Washington on Jan. 4 and spent the night in Nashville. On the road, Mr. Hardie said, they chatted about their families, politics and the fact that certain “people need to be taken out of government.”

When they arrived in Washington on Jan. 5, they checked into the Melrose hotel and left their weapons locked in the car, Mr. Hardie said. In the morning, Mr. Reffitt gave his partner a pair of plastic hand ties in case they “needed to detain anyone,” Mr. Hardie said.

The two men also donned their pistols, he said — Mr. Reffitt’s on his hip, Mr. Hardie’s under his armpit in a shoulder holster — and readied their rifles for action, leaving them in the cargo bay of the Equinox. Mr. Hardie told the jury that they were primarily concerned about “violence from these violent groups like antifa.”

After listening to Mr. Trump’s speech, Mr. Hardie said, he lost Mr. Reffitt in the crowd that was making its way toward the Capitol. The two met hours later at their hotel, he said, where Mr. Reffitt’s face was red from pepper spray and his legs were badly bruised from police projectiles.

Mr. Hardie said he was impressed by Mr. Reffitt’s story of confronting the police outside the building and urging the crowd to storm up a staircase leading toward the Senate chamber. He recalled that Mr. Reffitt had specifically mentioned an officer who fired several pepper balls at him and seemed to panic when he was undeterred.

He recounted for the jury what Mr. Reffitt said he told the officer: “Lady, I don’t want to hurt you, but every time you shoot me, I’m going to move forward.”

A sense of anxiety set in when the two men returned to Texas and discovered within days that the leader of the Texas Three Percenters had been detained by the authorities. In a group chat message to his compatriots, Mr. Reffit warned them to “be prepared,” adding, “THIS IS NOT A DRILL.”

When prosecutors asked Mr. Hardie about his reaction to the leader’s arrest, his answer was short and simple.

“Uh-oh,” he said.