Conventional wisdom has it that defendants never catch a break in US federal court: the conviction rate last year was more than 95%. But it seems those odds improve if, like the leaders of last winter’s armed standoff at the Malheur national wildlife refuge in Oregon, you are part of the radical anti-government right.

The decision by a Portland jury to acquit the Bundy brothers, Ammon and Ryan, and five others on conspiracy and firearms charges on Thursday night marks the third time in 28 years that a high-profile federal case involving armed anti-government agitators has collapsed.

In each case, questions have arisen over whether white nationalist agitators evoked sympathies among jurors that other defendants do not.

Four years ago, an attempt to charge members of the Hutaree Christian militia in Michigan with sedition ended in similar embarrassment for the government after the judge said there was no evidence the five defendants intended to attack anyone, much less murder a police officer and ambush his funeral as the prosecution alleged.

In 1988, another sedition trial in Fort Smith, Arkansas – this one featuring a rogue’s gallery of more than a dozen of America’s most visible far-right anti-government luminaries, some of them already serving long sentences for violent crimes – also led to acquittals all around, not to mention the marriage of a juror to one of the defendants.

In the wake of the Portland verdict, some civil rights advocates and anti-gun activists were quick to suggest a double standard when it comes to civil disobedience and attitudes to gun ownership.

“Apparently it’s legal in America for heavily armed white terrorists to invade Oregon,” the former TV talk show host Montel Williams wrote on Twitter. “Imagine if some black folk did this.”

On the other side of the political fence, some suggested the prosecutors may simply have overreached. Sedition is notoriously hard to prove and the charge has been leveled only a handful of times since the founding of the republic for that reason. In the Oregon case, one juror said he would have had no problem convicting the defendants of trespassing but the conspiracy charge, which carries much stiffer penalties, was a stretch.

In an age of anti-establishment anger, jurors also appear to have been swayed by the sheer confidence of the prosecuting attorneys.

“The air of triumphalism that the prosecution brought was not lost on any of us,” juror four wrote to the Oregonian newspaper, “nor was it warranted given their burden of proof.”

Mark Pitcavage of the Anti-Defamation League, one of America’s foremost authorities on rightwing extremism, said he could only imagine that courtroom dynamics along these lines had undone what had otherwise seemed like a very strong government case.

“I was hardly alone in thinking that,” he said. “The mere fact that many of the standoff defendants entered into plea deals rather than go to trial suggests that they and their attorneys also felt the government had a very strong case.”

There was similar incredulity at the not guilty verdicts in Fort Smith in 1988, as analysts pondered how the government could possibly lose a case against leaders and foot soldiers of the Ku Klux Klan and Aryan Nations, among other organizations, some of whom had previously been proven to have robbed banks and armored trucks, killed people, and openly called for the violent overthrow of the government.

On that occasion, the jury’s sympathy for the defendants was clear. One female juror started up a romance with defendant David Lane, previously convicted of murdering a talk-radio host in Denver. Another female juror ended up marrying David McGuire, charged with plotting to kill an FBI agent and a federal judge.

It didn’t help that the judge dispensed with standard jury selection and hand-picked an all-white panel over the objections of the prosecution.

“If we’d had good jury selection, I think we would have won the case,” the FBI agent targeted for assassination, Jack Knox, said in an interview years later. “The judge … was dredging right at the bottom of the barrel.”

Another former FBI agent with extensive experience of the radical far right, Danny Coulson, did not exclude the possibility of similar sympathies being at play in the Oregon case – on the side of law enforcement as much as the jury. Portland may be a liberal city, he said, but gun culture is deeply entrenched in Oregon and many people may have had some bedrock sympathy for the protesters’ complaints.

“It’s the tenor of the times,” Coulson said in an interview. “A lot of people in our country are sick of government trying to control every aspect of human life.

“I’m not saying I agree with that position, but there are a lot of people who make that case… The bureau [FBI] is brought into this stuff all the time, and they don’t want to do it. They don’t want to be brought into it, and they probably have some sympathy for the cause.”

Pitcavage did not agree that sympathy for far-right defendants was a given, in this or any other case.

“Almost every prosecution of rightwing extremism is successful,” he said. “Our prisons are full of rightwing extremists. It’s no more difficult to prosecute rightwing extremists than any other class of people. With any particular trial, though, there can be things that affect it.”