The criminal trial against Peter Navarro, a trade adviser to President Donald J. Trump, opened on Wednesday as prosecutors cast Mr. Navarro as deliberately stymying lawmakers in refusing to testify last year before the House committee investigating the Capitol attack.

In their opening statement, government lawyers repeatedly emphasized that the case against Mr. Navarro was relatively straightforward: Did Mr. Navarro show contempt for Congress when he disregarded the committee’s subpoena for documents and testimony?

“This case is just about a guy who didn’t show up for his testimony? Yes, this case is that simple,” a prosecutor, John Crabb Jr., said in Federal District Court in Washington. “But this case is also that important — we are a nation of laws, and Mr. Navarro acted like he was above the law.”

Lawyers for Mr. Navarro sought to paint him as a professional and well-educated policy adviser who simply got caught up in fraught legal negotiations with the Jan. 6 committee.

One of his lawyers, Stanley Woodward Jr., said that the Justice Department’s suggestion that Mr. Navarro was a critical witness to the House committee’s investigation was overstated, describing prosecutors’ opening statement as theatrical.

“It’s like one of those movies where you get nothing after the preview,” he said, while Mr. Navarro, who has spent the trial so far standing behind his lawyers’ table, continued to pace back and forth and listen intently.

Mr. Navarro, 74, faces two counts of contempt of Congress, making him the second top official of Mr. Trump’s to face criminal charges related to the former president’s efforts to stay in power. After Mr. Trump lost the 2020 race, Mr. Navarro turned his attention to obscure election law, drawing up last-ditch strategies to stall Congress’s certification of the election. If he is convicted, Mr. Navarro could face up to a year in jail and a fine of up to $100,000 for each count.

Prosecutors also called as witnesses several staff members on the Jan. 6 committee who helped draft and serve the subpoena to Mr. Navarro.

David Buckley, a staff director for the select committee, said the panel had hoped to interview Mr. Navarro under oath about his efforts to overturn the election. Of particular interest were a three-part report he wrote claiming widespread voter fraud in the 2020 election and a memoir published after he left the White House.

In the book, Mr. Navarro laid out a strategy, known as the Green Bay Sweep, to reject the results of the election in key swing states that had been called for Joseph R. Biden Jr. He described it as “our last, best chance to snatch a stolen election from the Democrats’ jaws of deceit.”

Mr. Navarro and his lawyers entered the trial shorn of their main defense: that Mr. Trump, who was no longer president at the time, had directed him to ignore the subpoena and that he was protected by executive privilege. Mr. Navarro has consistently maintained outside court that he was merely acting on the orders of Mr. Trump, who had expressly asked him and other senior advisers not to cooperate with the committee.

Last week, Judge Amit P. Mehta ruled that Mr. Navarro had not produced any clear evidence that he ever spoke to Mr. Trump about the subpoena, and therefore could not raise executive privilege as a defense.

That left Mr. Navarro’s lawyers forced to mount a more circuitous defense. Mr. Navarro had referred the House committee to Mr. Trump directly, they argued, but lawmakers did not follow up with him to confirm whether Mr. Navarro was covered by any privilege.