The judge questioned the credibility of his defense attorney. Prosecutors accused him of orchestrating a criminal conspiracy to influence the 2016 presidential election. And his former friend corroborated that accusation, providing hours of gripping testimony about his secret plot to protect his campaign.

Donald J. Trump’s criminal trial in Manhattan is off to an ominous start for the former president, and it may not get any easier in the days ahead.

The judge presiding over the case, Juan M. Merchán, is expected to rule soon on a request by prosecutors to hold Trump in contempt of court for attacking both witnesses and jurors. And the first witness, David Pecker, longtime editor of The National Enquirer, will return to the stand Thursday after the trial’s weekly break on Wednesdays.

Pecker, who was once close to Trump, is expected to face hours of additional questioning by prosecutors from the Manhattan district attorney’s office before Trump’s lawyers have a chance to question him.

Pecker has already provided some compelling testimony, transporting jurors to a crucial 2015 meeting with Trump and his fixer at Trump Tower in Midtown Manhattan.

Prosecutors called it the “Trump Tower conspiracy,” arguing that Pecker, Trump and Michael D. Cohen, who was then Trump’s personal lawyer and fixer, hatched a plot at the meeting to hide the looming sex scandals. Mr. Trump’s campaign.

Their efforts led Pecker’s tabloids to buy and bury two damaging stories about Trump. Cohen bought the silence of a porn star, a deal that is at the center of the case against the former president.

From the witness stand Tuesday, Pecker recalled how Cohen and Trump asked what he and his magazines (fixtures at American supermarket checkouts) could do “to help the campaign.” The account reinforced the prosecution’s argument that the men were protecting not only Trump’s personal reputation but also his political fortunes.

Pecker’s testimony came after a hard-hitting hearing for Trump and his legal team, as prosecutors argued that the trial is threatened by Trump’s repeated attacks on witnesses and jurors, mostly launched on social media and the website of his campaign. They urged Judge Juan M. Merchán to hold Trump in contempt for what they said were 11 violations of a gag order prohibiting the former president from attacking witnesses, prosecutors, jurors and court staff, as well as his family.

When Trump’s lead lawyer, Todd Blanche, claimed the former president was trying to comply, Judge Merchan rebuked him and responded in words no lawyer wants to hear: “You’re losing all credibility with the court.”

The case against Trump, the first US president to face a criminal trial, centers on Cohen’s $130,000 payment to porn star Stormy Daniels to maintain her silence. Prosecutors say she paid Daniels at Trump’s direction during the 2016 campaign to keep her quiet about a sexual tryst she said she had with Trump. He denies having had sexual relations with her.

Trump, who faces up to four years behind bars if convicted, is charged with 34 counts of falsifying business records for the way he accounted for the $130,000 payment to Cohen. Each charge reflects a different fake check, ledger and invoice that prosecutors say Trump used to disguise the true purpose of the refund.

Trump, 77, who is once again the presumptive Republican nominee, faces three other criminal cases in three different cities on charges of conspiring to overturn his 2020 election loss and mishandling classified records once he was no longer president. But with those cases delayed, the Manhattan case may be the only one that goes to trial before Election Day.

The Manhattan case, in only its sixth day, has become a political and media spectacle as Trump’s campaign-style attacks on Cohen and the jury test the limits of the legal system and the judge’s patience.

The gag order hearing, held with the jury outside the courtroom, demonstrated a jarring reality for Trump as he seeks to reclaim the White House while impeached: his political reflexes and the norm-breaking spirit that has defined Trump. era, often clash with the letter of the law.

Witnesses in the case “rightly fear” being subjected to the former president’s “virtriole,” prosecutor Christopher Conroy told the judge. He recited statements that Manhattan prosecutors believe crossed the line, including calling Mr. Cohen and Ms. Daniels “sleazy bags” and reposting an attack on the jury. That happened the night before an already seated juror asked to be excused.

“What happened here was exactly what this order was intended to prevent, and the defendant doesn’t care,” Mr. Conroy said.

Trump’s lawyer, Todd Blanche, argued that Trump’s posts were not personal and did not violate the order, because he was simply responding to “a barrage of political attacks.”

But Judge Merchan became furious and implored Blanche to stick to the facts and the law.

“I need to know what is true,” Judge Merchan said, underscoring Trump’s penchant for using social media to spread lies.

Then the situation got worse for Blanche, who seemed taken aback by the judge. At one point, Judge Merchan called one of his arguments “silly.”

Prosecutors have asked Judge Merchan to fine Trump $1,000 for each statement, although Conroy wondered aloud whether Trump, who has sold campaign merchandise with his mugshot, was actually looking to go to jail. The judge, whose daughter has been among Trump’s targets, did not immediately rule.

The case against Trump began Monday, with both sides delivering opening statements that offered competing views of Trump and the evidence. A prosecutor accused the former president of orchestrating a “criminal conspiracy and cover-up.” Trump’s lawyer proclaimed: “President Trump is innocent.”

The prosecution then called its first witness, Mr. Pecker, who returned to the stand Tuesday for a second day of testimony.

In about two and a half hours of questioning Pecker on Tuesday, prosecutors placed him firmly in Trump’s orbit, as a longtime admirer and friend who became an extension of Trump’s 2016 campaign. His closeness to Trump — and his kind, almost grandfatherly affection – seemed to reinforce his credibility.

“I would call him Donald,” Pecker recalled, adding that he had “a great relationship with Trump over the years” and had launched a magazine with him called “Trump Style.”

Pecker described a symbiotic relationship between Trump and The National Enquirer during the former president’s turn as a reality TV host on “The Apprentice.” Trump would leak details of the show to the magazine, which would in turn publish stories about the contestants.

The relationship rose to national prominence after the crucial 2015 meeting at Trump Tower.

“I got a call from Michael Cohen telling me the boss wanted to see me,” Pecker told the jury.

Afterward, Cohen routinely contacted Pecker, communicating weekly or even daily. The purpose of their conversations was often to protect Trump from negative stories, including a bouncer’s apparently false claim that Trump had fathered a child out of wedlock. Pecker, who bought the story, testified that Cohen had told him that “the boss would be very happy” to have that story suppressed.

Pecker, who later also bought a story from a former Playboy model who said she had an affair with Trump, explained that Cohen was “physically in every aspect of whatever the campaign was working on.” But, in a detail the defense can seize on, she testified that Cohen, who was not a campaign employee but Trump’s personal lawyer, may have “injected himself” into the campaign at times.

Trump’s lawyers have not yet questioned Pecker, but when they do, they will likely seize on that description of Cohen. A central theme of Trump’s defense is to portray Cohen as a renegade and a liar, and to distance the former president from the most problematic evidence.

However, Pecker’s testimony placed Trump squarely in the middle of his conspiracy. And in a sign that at least Pecker knew his deal was problematic, he noted that he wanted to keep it “confidential.” When prosecutor Joshua Steinglass asked why, Pecker explained that he didn’t want it to “leak” that he had helped the campaign.

When questioned, Pecker acknowledged that he not only published harmful stories but also promoted useful ones. Cohen, he explained, would provide him with information about Trump’s Republican primary opponents, and The National Enquirer would sometimes “embellish” them.

The tabloid, for example, published articles about Trump’s main opponents, including Ben Carson, Ted Cruz and Marco Rubio. Prosecutors illustrated the point for jurors, posting several lurid headlines on the screens: “Donald Trump Blasts Ted Cruz’s Father Over Photo with Assassin JFK,” “Blundering Surgeon Ben Carson Left Sponge on Brain of a patient!” and, in a moment of ironic foreshadowing, “Ted Cruz shamed by a porn star.”

At the Trump Tower meeting, Pecker said, he had indicated that he expected many women would “come out and try to sell their stories” about Trump, because he was known as “the most eligible bachelor and dating the most beautiful woman.” women.”

In fact, Trump was not single. He had married his third and current wife, Melania Trump, in 2005.

Kate Christobek, Alan Feuer, Wesley Parnell and Jesse McKinley contributed reports.