Former Trump White House adviser Peter Navarro will not be able to argue before a jury at his contempt of Congress trial next week that the former president asserted privilege to shield him from a House January 6 committee subpoena, a federal judge ruled Wednesday.

Navarro had not met the burden to establish that Donald Trump formally granted executive privilege or testimonial immunity, US District Judge Amit P. Mehta said at a pre-trial conference.

Mehta announced the ruling after holding an evidentiary hearing Monday during which Navarro testified about alleged assertions from Trump.

Navarro's criminal case, which was brought by the Justice Department in June 2022, goes to trial next Tuesday. Navarro has pleaded not guilty to the charges, and Mehta's new ruling severely hamstrings the arguments the former Trump aide will be able to present in his defense.

In a lengthy explanation of his ruling delivered from the bench Wednesday, Mehta said he concluded that either Trump himself or someone authorized to assert privilege or immunity on his behalf would have had to personally invoke the privilege for it to be validly asserted. The judge said Navarro had not put forward adequate evidence to show such an assertion when he was subpoenaed for testimony and documents by the House committee in February 2022.

"The privilege cannot be validly asserted by mere acquiescence," Mehta said.

Navarro, speaking to reporters after Wednesday's hearing, said Mehta's ruling concerned "very complex and important constitutional issues related to the separation of powers between the legislative branch and the executive branch."

He previewed the possibility that Mehta's conclusions would ultimately be appealed.

"These are questions that will certainly move up the chains -- the appellate level. And as I said at the beginning, this is probably going to the Supreme Court because this is so important," Navarro said. "You can't have a Congress, a partisan Congress, that abuses the subpoena process for the purpose of punishing the party that's out of power."

Navarro's "nondescript" testimony earlier this week about a February 20, 2022, call during which Trump supposedly asserted the privilege lacked "specificity," the judge said.

"The lack of detail -- in my view -- of that testimony is telling," Mehta said. The judge also pointed to the lack of follow-up from Trump to Congress after the House voted to hold Navarro in contempt that April, suggesting that Trump could have communicated to the lawmakers that he had asserted privilege to correct the House's record.

"That silence strongly corroborates" that there was no formal invocation of privilege, Mehta said.

The case was initially scheduled to go to trial earlier this year, but it was delayed so that Mehta could consider whether the evidence about Trump's supposed assertions could be presented.

During Monday's hearing, Navarro testified that in conversations with Trump following the issuance of the committee subpoena on February 9, 2022, the former president made it known that he didn't want Navarro to cooperate with the panel.

"It was clear during that call that privilege was invoked -- very clear," Navarro said at one point, referring to the February 20, 2022, call.

"There was no question that the privilege had been invoked from the get-go -- none," he added later.

But the judge appeared highly skeptical of Navarro's assertions after his testimony had concluded, saying of the February call: "I still don't know what the president said."

"That's pretty weak sauce," the judge said later, referring to a comment Navarro said Trump made about regretting not letting him testify. The comment had been used by Navarro and his team to bolster their argument that Trump did invoke privilege because his subsequent regret indicated as much.

This story has been updated with additional information.