Former White House adviser Peter Navarro has reported to prison for a contempt of Congress conviction, becoming the first senior Trump administration official to be locked up for a crime related to the January 6, 2021 attack on the Capitol.

Navarro was sentenced to four months in prison for defying a subpoena for documents and a deposition from the House committee that investigated the riot by supporters of then-President Donald Trump.

Navarro was defiant on Tuesday in remarks to reporters before he headed to the federal prison in Miami, calling his conviction the “partisan weaponisation of the judicial system”.

He has maintained that he could not co-operate with the committee because Trump had invoked executive privilege. But courts have rejected that argument, finding Navarro couldn’t prove Trump had actually invoked it.

“When I walk in that prison today, the justice system – such as it is – will have done a crippling blow to the constitutional separation of powers and executive privilege,” Navarro told reporters Tuesday.

Navarro, who served as a White House trade adviser under Trump, was subpoenaed by the committee over his promotion of false claims of voter fraud in the 2020 election in the run-up to the Capitol attack.

Navarro had asked to stay free while he appealed his conviction to give the courts time to consider his challenge. But Washington’s federal appeals court denied his bid to stave off his sentence, finding his appeal wasn’t likely to reverse his conviction.

And Supreme Court Chief Justice John Roberts on Monday also refused to step in, saying in a written order that he has “no basis to disagree” with the appeals court. Roberts said his finding doesn’t affect the eventual outcome of Navarro’s appeal.

Navarro was the second Trump aide convicted of contempt of Congress charges. Former White House adviser Steve Bannon previously received a four-month sentence but a different judge allowed him to stay free pending appeal.

The House committee spent 18 months investigating the insurrection, interviewing more than 1000 witnesses, holding 10 hearings and obtaining more than one million pages of documents.

In its final report, the panel ultimately concluded that Trump criminally engaged in a “multi-part conspiracy” to overturn the election results and failed to act to stop his supporters from storming the Capitol.

Special counsel Jack Smith has separately charged Trump with conspiring to overturn his election loss to President Joe Biden. That case is on hold while the Supreme Court weighs Trump’s claim that he is immune from prosecution. The high court is scheduled to hear arguments on the matter next month.