Stewart Rhodes, the founder of the far-right Oath Keepers militia, was sentenced on Thursday to 18 years in prison, after being convicted of seditious conspiracy for his role in the January 6 attack on Congress.

Related: Proud Boys and Oath Keepers: what is their future with top leaders jailed?

Prosecutors sought a 25-year term. Lawyers for Rhodes said he should be sentenced to time served, since his arrest in January 2022.

Before handing down the sentence on Thursday, the judge told a defiant Rhodes that he posed a continued threat to the US government, saying it was clear Rhodes “wants democracy in this country to devolve into violence”.

“The moment you are released, whenever that may be, you will be ready to take up arms against your government,” US district judge Amit Mehta said.

Speaking shortly before he was sentenced, Rhodes claimed the prosecution was politically motivated.

“I’m a political prisoner and like President Trump my only crime is opposing those who are destroying our country,” he said.

Rhodes also noted that he never went inside the Capitol on January 6 and insisted he never told anyone else to do so.

But members of the Oath Keepers took an active role on 6 January 2021, when a mob incited by Donald Trump smashed its way into the Capitol, attempting to stop certification of Joe Biden’s election win.

Prosecutors successfully made the case that Rhodes and his group prepared an armed rebellion, including stashing arms at a Virginia hotel, meant for quick transfer to Washington DC.

Other members of the Oath Keepers, some convicted of seditious conspiracy, are due to be sentenced this week and next. Members of another far-right group, the Proud Boys, will face sentencing on similar convictions later this year.

Nine deaths have been linked to the January 6 attack, including suicides among law enforcement. More than 1,000 arrests have been made and more than 500 convictions secured.

In court filings in the Oath Keepers cases, prosecutors said: “The justice system’s reaction to January 6 bears the weighty responsibility of impacting whether January 6 becomes an outlier or a watershed moment.”

At Thursday’s hearing, speaking for the prosecution, the assistant US attorney Kathryn Rakoczy pointed to interviews and speeches Rhodes has given from jail repeating the lie that the 2020 election was stolen and saying it would be stolen again in 2024.

In remarks just days ago, Rhodes called for “regime change”, Rakoczy said.

People “across the political spectrum” want to believe January 6 was an “outlier”, Rakoczy said. “Not defendant Rhodes.”

A defense lawyer, Phillip Linder, denied Rhodes gave any orders for Oath Keepers to enter the Capitol on January 6. But he told the judge Rhodes could have had many more Oath Keepers come to the Capitol “if he really wanted” to disrupt certification of the electoral college vote.

In a first for a January 6 case, Judge Mehta agreed with prosecutors to apply enhanced penalties for “terrorism” under the argument that the Oath Keepers sought to influence the government through “intimidation or coercion”.

Judges in previous sentencings had shot down the justice department request for the so-called “terrorism enhancement”, which can lead to a longer prison term, but Mehta said it fitted Rhodes’s case.

“Mr Rhodes directed his co-conspirators to come to the Capitol and they abided,” the judge said.

Like all other forms of Trump’s attempted election subversion, the attack on Congress failed.

In the aftermath of the attack, after he had left office, Trump was impeached for a second time, for inciting an insurrection. He was acquitted by Senate Republicans.

Laying out Trump’s actions after the 2020 election, the House January 6 committee made four criminal referrals to the justice department.

Trump still faces potential indictments in state and federal investigations of his election subversion and role in the attack on Congress.

Nonetheless, he remains the clear frontrunner for the Republican presidential nomination next year.