It is the longest sentence handed down so far to any participant in the January 6 riot, which sought to overturn former President Donald Trump’s loss in the 2020 election.

But the sentence nevertheless falls short of the 25 years the prosecution sought in the case, contending that Rhodes remains a danger to US democracy.

US District Judge Amit Mehta acknowledged that argument as he announced his decision, saying that Rhodes, 58, does indeed represent an “ongoing threat”.

“For decades, Mr Rhodes, it is clear you have wanted the democracy of this country to devolve into violence,” Mehta said in handing down the sentence.

“The moment you are released, whenever that may be, you will be ready to take up arms against your government.”

Rhodes, who was convicted of seditious conspiracy in November, told the court before sentencing on Thursday that he was being treated as a “political prisoner”.

He has denied instructing members of the Oath Keepers to attack the Capitol, and in his statement, he declared his only intent was to protect the US from the people “who are destroying our country”.

Using a term for January 6 participants — “J6er” — Rhodes also denounced the criminal charges brought against him and at least 950 other defendants.

“I believe this country is incredibly divided,” he told the court. “And this prosecution — not just of me, but of all J6ers — is making it even worse. I consider every J6er a political prisoner and all of them are being grossly overcharged.”

Judge Mehta addressed those concerns directly in his sentencing remarks: “You are not a political prisoner, Mr Rhodes.”

The length of Thursday’s sentence also includes an enhancement for “terrorism”, another first for a January 6 case.

Judges in separate cases have denied requests from the Department of Justice to apply a “terrorism enhancement”, as punishment for attempting to intimidate or coerce the government.

In pursuing the longer sentence, Assistant US Attorney Kathryn Rakoczy pointed to statements Rhodes made from jail calling the 2020 election stolen and casting doubt on the upcoming 2024 presidential race.

Those statements, she argued, indicated that Rhodes did not feel January 6 was an “outlier”.

Defence lawyer Phillip Linder, meanwhile, announced his client would appeal his conviction. He maintained Rhodes was being used as a scapegoat.

“If you want to put a face on J6, you put it on Trump, right-wing media, politicians, all the people who spun that narrative,” Linder said.

Kelly Meggs, a leader of the Florida chapter of the Oath Keepers who was convicted of seditious conspiracy alongside Rhodes in November, was also sentenced on Thursday. He received 12 years in prison.

“I truly apologize for being here,” Meggs told the court, crying. “It has not only destroyed my life but the life of my entire family.”

The two men’s convictions for seditious conspiracy in November were rare in the US justice system. Prior to the Oath Keepers trial, the last time the Department of Justice pursued a seditious conspiracy case was in 2010 — and it failed.

The last successful prosecution had been in 1995, in the wake of a foiled plot to blow up the United Nations headquarters in New York City, among other structures.

But since the Oath Keepers’ convictions, the Department of Justice has successfully convicted four members of the far-right group Proud Boys of seditious conspiracy as well, for their roles in the January 6 attack. They include group leader Enrique Tarrio.

Thursday’s sentencing has been seen as a bellwether for the Proud Boys’ own potential prison terms. They are due to be sentenced in August and September.

Before Rhodes’s 18-year sentence, the longest prison term handed to a participant in the January 6 attacks had been 14 years.

Earlier this week, a Texas winery operator, Christopher Ray Grider, was given seven years for storming the US Capitol. Prosecutors in Grider’s case argued he was responsible for “setting in motion” a series of events that led to the death of a fellow rioter.

The Oath Keepers — a group named for their “oath” to defend the Constitution — have been accused of employing a military-style stack formation to break into the Capitol on January 6.

Prosecutors also allege that the group maintained a stash of weapons at a Virginia hotel near Washington, DC, so that “quick reaction force” groups could use them if necessary.

More than 1,000 people have been arrested in connection with the January 6, 2021 riot, according to the Department of Justice, with more than half of them, 570, pleading guilty to federal charges.