“A publisher cannot be held liable for commentary based on public facts,” said Brian Hauss, a lawyer with the American Civil Liberties Union.
Frederick Schauer, a law professor at the University of Virginia, said public figures who sue for libel must show that a publisher either “knew it was false before publishing, or had actual suspicion of falsity and went ahead anyway.” Proving that in court, he said, “is virtually impossible.”
The lawsuit was filed on behalf of the Trump campaign by Charles J. Harder, a lawyer with a reputation for waging aggressive legal battles against prominent news organizations.
Mr. Harder is best known for representing Terry G. Bollea, the former professional wrestler known as Hulk Hogan, in a lawsuit against Gawker Media that was secretly underwritten by the tech investor Peter Thiel. The suit, which concerned the publication of a sex video, resulted in a $140 million decision that led to Gawker Media’s bankruptcy and forced the site’s sale.
Mr. Harder also represented Melania Trump, Mr. Trump’s wife, when she sued The Daily Mail, a British tabloid, in 2016 over what she said were “false and defamatory statements,” including that a modeling agency she worked for in the 1990s was also an escort service. The Daily Mail ultimately apologized, retracted the article and paid damages in a settlement.
This is not Mr. Trump’s first time going to court against a journalist. In 2006, he sued Timothy L. O’Brien for libel after the publication of Mr. O’Brien’s biography, “TrumpNation: The Art of Being the Donald.” The case was dismissed three years later. (Mr. O’Brien, who previously worked as a reporter and editor at The Times, is a senior adviser to Michael R. Bloomberg’s presidential campaign.)
The Times is also defending itself in a defamation suit brought by Sarah Palin, the former Republican vice-presidential nominee, over an editorial published in the Opinion pages that incorrectly linked her to a 2011 mass shooting that severely wounded Representative Gabrielle Giffords of Arizona. Ms. Palin’s case was dismissed by a Federal District Court, but an appellate court reinstated the suit last year.
Nicole Hong contributed reporting, and Alain Delaquérière contributed research.