Stormy Daniels’s testimony on Tuesday against Donald J. Trump at his criminal trial in Manhattan was not the first time that the porn star and the former president have clashed in court.

Six years ago, Ms. Daniels — then known by her off-camera name, Stephanie Clifford — filed a defamation lawsuit against Mr. Trump that ultimately failed, leading to damaging consequences for both her and her lawyer.

The lawsuit, first filed in Manhattan federal court in April 2018 and then transferred to California, accused Mr. Trump of posting a social media message that called into question Ms. Daniels’s credibility.

It came in response to one of her own posts, in which she included a sketch of a man who, she said, had threatened her in a Las Vegas parking lot in 2011, telling her to keep silent when she was first considering revealing her account of having had sex with Mr. Trump.

In his tweet, Mr. Trump called the sketch “a total con job,” saying it depicted “a nonexistent man.” A lawyer who represented Ms. Daniels at the time, Michael Avenatti, called Mr. Trump’s statements an attack for which she should be compensated. He cited “harm to her reputation, emotional harm, exposure to contempt, ridicule, and shame.”

On Tuesday, Ms. Daniels briefly mentioned the threatening episode from the witness stand, saying that she did not report it when it happened because it would have been upsetting to her partner at the time. But she has not yet testified about the defamation lawsuit.

Within six months of the suit’s filing, a federal judge dismissed it, ruling that Mr. Trump’s post was an example of the “‘rhetorical hyperbole’ normally associated with politics and public discourse in the United States.”

“The First Amendment protects this type of rhetorical statement,” the judge, James S. Otero, wrote in his decision.

Judge Otero ordered Ms. Daniels in 2018 to reimburse Mr. Trump for the more than $100,000 he spent in legal fees to defend himself.

Months later, Ms. Daniels and Mr. Avenatti lost another lawsuit against Mr. Trump. This one, also brought in California, had sought to release Ms. Daniels from a nondisclosure agreement that is now central to the criminal trial in Manhattan. As part of that arrangement, she received $130,000 through Mr. Trump’s personal lawyer at the time, Michael D. Cohen.

While representing Ms. Daniels, Mr. Avenatti rose to such fame that he became a staple of the cable news circuit and at one point even considered running for president. But the consequences of losing the suits were even more severe for him than for his client.

Once joined at the hip, he and Ms. Daniels had a fiery falling out and she eventually accused him of stealing more than $300,000 in book payments meant for her. Those accusations led to a trial in Manhattan, where in 2022, Mr. Avenatti was convicted of wire fraud and aggravated identity theft and ultimately sentenced to four years in prison.

Mr. Avenatti remains behind bars, serving terms for two other theft and tax evasion convictions, but he recently weighed in on Mr. Trump’s own case in Manhattan.

On April 10, he posted a social media message attacking Ms. Daniels and Mr. Cohen, who is also expected to testify in the case, saying it was “outrageous” that they were permitted to go after Mr. Trump, but Mr. Trump could not react because of a gag order imposed on him.

Mr. Trump, appearing to appreciate the support, responded online to Mr. Avenatti.

“Thank you Michael Avenatti,” he wrote, “for revealing the truth about two sleaze bags who have, with their lies and misrepresentations, cost our Country dearly!”