“Are these your posts?” the judge asked.
The slight, silver-haired woman stood at a lectern in the icy-cold courtroom on the 15th floor of the Manhattan Criminal Courts Building. She blinked under the lights as she was questioned, standing about 12 feet from the man who had inspired the social media messages nearly a decade before.
They were hers, she confirmed, and the judge directed her to read them aloud. It took her a moment to get to the crux of the first, which dated back to 2016.
“Let’s be civil,” she read. “And try to protect the rights of the many at risk should we fail to stop the election of a racist, sexist, narcissist …” She interrupted herself. “Oops. That sounds bad.”
It was just one of several such inquisitions this week as lawyers and the judge asked prospective jurors, who live in deeply Democratic Manhattan, to explain social media posts that were critical of him as president or as a candidate. The posts were apparently unearthed by researchers working for the legal team representing Donald J. Trump.
Prosecutors asked their own questions, but for the most part did not delve into the prospective jurors’ posting histories. It was the defense team that expressed the most concern about what had happened online, an appropriate focus for lawyers representing the most online of presidents.
Mr. Trump thrived on social media. Using Twitter, a platform that began pushing itself as a breaking news source the year before the 2016 election, he created a sense for his followers that he was speaking directly to them. He also used the platform for slashing attacks on rivals, promoting his own thoughts or positions on news of the day, and to shape the perception of the campaign.
But, in retrospect, many posts from that era — from political operatives, from civilians and from journalists — “sound bad,” as the prospective juror put it. The 2016 election was the first in which the social internet, having reached full maturity, played a central role.
The social internet has evolved in rapid stages, and the eight years between 2016 and 2024 might as well be an eon. Twitter, now owned by the billionaire Elon Musk and renamed X, has become less of a central force in political conversation, and awareness of the toxicity of social media is broader.
Many people have publicly questioned why they spent so much time making comments on social media. Over the past week, some jurors who were confronted with their old posts seemed sheepish, if not outright embarrassed.
That happened to the prospective juror who had called Mr. Trump sexist and racist. Identifying herself as a “Bernie gal,” who had supported the presidential candidacy of Senator Bernie Sanders, she first defended herself.
“Electoral politics can get pretty spicy,” she said. “And Mr. Trump can get pretty spicy with his politics sometimes too.”
But then she apologized to Mr. Trump for the tone of the posts, underscoring how infrequently people have to interact personally with someone they criticize online. “I have stopped making such harsh political posts,” she said. She maintained that she could be a fair juror, but the defense used a challenge to dismiss her.
Other posts, some from Facebook, also came up. One prospective juror, known as B38, wrote, “Watch out for stupid tweets by DJT,” and, apparently once Mr. Trump was elected, “get him out and lock him up.” He was brought into the courtroom, and told the judge that he could put his views aside and be fair. But he was dismissed.
Another prospect found her husband’s old posts placed under the microscope. One was a screen grab of a video showing actors who play members of the Avengers, a group of Marvel superheroes, as they “unite against Donald J. Trump.”
(Someone else replied with the riff, “the Avengers unite against Donald Trump, and to get Mark Ruffalo naked,” referring to the reluctant promise by the actor who plays the Hulk to do a nude scene in his next movie if viewers turned out at the polls.)
That juror, too, was dismissed.
Mr. Trump’s own posts are not off limits. The Manhattan district attorney’s office sought to introduce several tweets from his presidency, in which he first defended and then attacked his former fixer Michael D. Cohen, who paid $130,000 in hush money to Stormy Daniels. Mr. Trump is charged with falsifying business records to cover up reimbursements for that payment.
The judge said that the prosecution would likely be allowed to show the former president’s old posts to jurors.
“It’s going to be hard to convince me that something that he tweeted out to millions of people voluntarily cannot be used in court,” he said.
Mr. Trump’s posting style has not changed much; if anything, it has become darker since he was banned from X after the Jan. 6, 2021, attack on the U.S. Capitol by a pro-Trump mob seeking to stop the certification of President Biden’s election. (Mr. Trump was reinstated by Mr. Musk, but has since started his own social media site, Truth Social, where he posts frequently.)
On Thursday, as court concluded for the day, a Trump lawyer, Todd Blanche, asked to be told who the prosecution’s first three witnesses would be. But prosecutors refused, noting that the former president had consistently attacked witnesses on social media.
Mr. Blanche asked the judge whether he could be allowed to promise that Mr. Trump wouldn’t post about witnesses.
Justice Merchan was dubious.
“I don’t think you can make that representation,” he said.
