President Donald Trump’s reelection campaign sued The New York Times for libel today, alleging that an op-ed article published by the newspaper falsely asserted a “quid pro quo” between Russian officials and Trump’s 2016 campaign.

Trump often threatens to sue media organizations but rarely follows through. The lawsuit, filed in New York state court in Manhattan, is the first time his political operation has taken legal action against an American news outlet since he took office.

The lawsuit concerns an essay published by the Opinion section of The Times in March 2019. The article, headlined “The Real Trump-Russia Quid Pro Quo,” was written by Max Frankel, who served as executive editor of The Times from 1986 to 1994. (The Opinion section of The Times operates separately from its newsroom.)

In the essay, Frankel wrote about communications between Trump’s inner circle and Russian emissaries in the lead-up to the 2016 election. He concluded that, rather than any “detailed electoral collusion,” the Trump campaign and Russian officials “had an overarching deal”: “the quid of help in the campaign against Hillary Clinton for the quo of a new pro-Russian foreign policy.”

The Trump lawsuit argues that this conclusion “is false” and that The Times published the essay “knowing it would misinform and mislead its own readers.” The suit also accuses The Times, without evidence, of harboring “extreme bias against and animosity toward” Trump’s reelection campaign.

The Times responded today that it would fight the suit.

“The Trump campaign has turned to the courts to try to punish an opinion writer for having an opinion they find unacceptable,” Eileen Murphy, a spokeswoman for The Times, said in a statement.

“Fortunately, the law protects the right of Americans to express their judgments and conclusions, especially about events of public importance,” Murphy added. “We look forward to vindicating that right in this case.”

Trump, whose vilification of the news media has little precedent among past presidents, has ratcheted up his attacks on the press over the past year. He has accused The Times of “treason,” tweeted the term “fake news” hundreds of times and threatened to pull broadcast licenses.

Asked about the lawsuit at a news conference at the White House tonight, Trump doubled down on his criticism of The Times. “It’s beyond an opinion,” he said of Frankel’s op-ed article. “That’s not an opinion. That’s something much more than an opinion.”

“They did a bad thing,” the president added, “and there’ll be more coming.”

Earlier today, several media law experts reacted with skepticism about the Trump campaign’s chances of succeeding in the suit.

“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.

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 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.

Harder also represented Melania Trump, 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 Trump’s first time going to court against a journalist. In 2006, he sued Timothy L. O’Brien for libel after the publication of O’Brien’s biography, “TrumpNation: The Art of Being the Donald.” The case was dismissed three years later. (O’Brien, who previously worked as a reporter and editor at The Times, is a senior adviser to Michael 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 Rep. Gabrielle Giffords of Arizona. Palin’s case was dismissed by a U.S. District Court, but an appellate court reinstated the suit last year.