Former President Donald Trump is not expected to testify on behalf of his former trade adviser Peter Navarro, potentially undercutting a key defense for Navarro in his upcoming criminal trial on contempt of Congress charges for defying the House select committee that investigated the US Capitol attack on January 6, 2021.

A lawyer for Navarro, Stanley Woodward, said in a court hearing Friday that Navarro's legal team -- which includes several former and current lawyers around the former president -- had talks with Trump's legal team but don't expect to call Trump as a witness.

Woodward did not say why Trump wouldn't take the stand, but the former president is campaigning to return to the White House and also faces a busy list of criminal cases and lawsuits that he is fighting as a defendant.

The absence of Trump's testimony could leave Navarro, who has pleaded not guilty, without direct evidence that he was acting at the direction of the former president when he declined to testify and turn over records to Congress. Navarro has claimed Trump told him to assert executive privilege to keep matters related to the former president and top White House advisers confidential, and that Trump passed the message through one of his aides, Liz Harrington.

Navarro seeks to have Harrington testify for his case, though she already was called by prosecutors to speak to a grand jury investigating Navarro, according to records in his case.

On Friday, Navarro's legal team discussed the possibility of bringing in testimony from Harrington about the former president's instructions to Navarro at a hearing later this month. Woodward described Harrington at one point as a "critical witness."

Navarro's case may be a major test for congressional authority and the reach of the presidency. The trial would follow the conviction by a jury of another former Trump adviser, Steve Bannon, on the same charges last year. Bannon is appealing.

Navarro's criminal case is set to go to trial in early September. In addition to serving as trade adviser in Trump's White House, he handled some of the administration's coronavirus response efforts. He also publicly discussed efforts to overturn Trump's election loss in 2020.

The federal judge overseeing the case, Amit Mehta of the DC District Court, said he was "not swayed" by Navarro's attorneys' attempts to move the trial date back and that he was "highly disinclined" to move the date of Harrington's testimony.