I don’t know whether our first president actually said “I cannot tell a lie,” but I do know that defamation law is experiencing a resurgence of “liar” cases, including one against our current president.

That case is being brought by a woman named Sumner Zervos, who appeared on “The Apprentice” more than a decade ago. During the 2016 presidential campaign, she held a news conference and accused Mr. Trump of uninvited kissing and touching. Trump repeatedly said and tweeted that it never happened, effectively calling Ms. Zervos a liar.

Her response was to sue him for libel, and a New York judge recently denied Trump’s motion to toss the case out of court. He is appealing that ruling.

Stephanie Clifford (“Stormy Daniels”) has brought a similar libel case against Trump lawyer Michael Cohen. Other women have sued Bill O’Reilly, former Alabama senatorial candidate Roy Moore, and Bill Cosby, among others. The scenario is familiar. A woman accuses a public figure of sexual misconduct. The man denounces his accuser in the media. Mr. Trump even threatens to sue them all.

Several Supreme Court decisions bear on whether these members of the #MeToo movement can prevail in court. One is New York Times v. Sullivan (1964), the Court’s most far-reaching defamation case. If the woman is a “public figure,” she has to show that her accuser knowingly made a false accusation or acted with “reckless disregard” of the truth.

Clifford is obviously a public figure. Zervos and others are not as well known, but according to a recent decision by the federal appeals court in Boston, once a woman conducts an interview with a reporter (in that case discussing Bill Cosby), she “thrusts herself” into a “public controversy” and becomes a public figure as well.

In Milkovich v. Lorain Journal (1990), a reporter accused a hockey coach of lying, and the question was whether this was a protected opinion or an actionable statement of fact. The Court ruled that there is no wholesale libel immunity for opinions. If they rely on undisclosed false facts, then the case can go forward.

The bedrock principle of all libel cases is that the offending statement must be provably false. Decades ago, under common law, the libel defendant had the burden of proving truth. Philadelphia Newspapers v. Hepps (1986) changed that as a matter of First Amendment protection and held that it is now up to the plaintiff to prove falsity.

It’s easy to understand why Trump hasn’t sued his accusers. If he did, he would have to persuade a jury that their accusations of misconduct were false. And, as a public official, he would have to prove by “clear and convincing” evidence that they lied on purpose.

The irony is that in most of these cases (Bill Cosby being an exception), it is too late to bring criminal charges, or for the women to bring civil assault cases. Once these men decided to go public, however, they opened a courtroom door that would otherwise have remained closed. They have managed to unring a bell.

Judicial reactions have been mixed. Some claims have been dismissed, while others are bogged down in the pre-trial stage. Insofar as Trump is concerned, Clinton v Jones (1997) established that even a sitting president can be sued for acts committed before he took office. So, unless the ruling in Zervos’s case is overturned, he will either have to settle the case or show up in court to defend himself.

How will these cases turn out? The Supreme Court has provided little guidance, and the use of Twitter and other means of social media communication complicates the problem. We do not know whether the courts will act more permissibly when it comes to communication by social media, effectively giving a freer hand to those who make spur-of the-moment accusations. This counter-intuitive approach would be unfortunate but not entirely novel. The law already gives more leeway to publications that do not check their facts than to those who do.

Whether an accusation of lying is libelous goes back to Washington’s time. In 1793, a Connecticut court threw its arms into the air and was simply unable to decide whether calling someone identified only as “Captain Riggs” a “damned liar” was defamatory. In 1812, a Pennsylvania judge had no problem declaring that “everyone knows” it is not. But in 1900 a Georgia court said the opposite, finding it “difficult to imagine” a greater stain on one’s reputation than being called a liar.

The Milkovich case holds the key. On what truthful facts did the reporter rely when he wrote that the hockey coach lied? He didn’t say. Someone who accuses a person of lying, even if that is an opinion, presumably has supporting information. Under that decision, he should disclose the facts so that the reader can make up his or her own mind.

A week after the “Access Hollywood” tape became public and candidate Trump called it “locker room talk,” Zervos gave her press conference. Trump went on a tweet storm, using such words as “100% fabricated,” “outright lies,” and “totally made up.” Similarly, after the public learned of his $130,000 payment to Clifford, Cohen released a statement that the Stormy-Donald “affair” never happened, which she says was the same as calling her a liar.

If today’s courts agree with the 1900 Georgia decision, and if these women can get past the legal and factual obstacles that public figure plaintiffs face, they will eventually have their day in court. In that event, Trump, Cohen, and others will have their hands full.