It is not uncommon for high-profile allegations against celebrities to prompt defamation lawsuits, but they are usually filed by the star against the accuser.
In 2014, however, Joseph Cammarata, the attorney for Cosby accuser Tamara Green, realized he could adapt that strategy for his own purposes after Cosby's lawyer issued a statement calling the allegations "fantastical."
Like many other Cosby accusers, Green was unable to sue for assault because the alleged incident occurred decades ago.
"A direct claim for the assault is not available, so I came up with the idea that a defamation claim would be the appropriate vehicle to use to address the underlying harm," said Cammarata, whose lawsuit now includes seven Cosby accusers as plaintiffs. All told, 10 Cosby accusers filed four defamation lawsuits in three states.
In simple terms, the argument is that Trump and Cosby have effectively branded the women as liars by denying the incidents occurred. But the women face a difficult challenge in making their cases, experts say.
"Merely saying, 'I didn't do it,' is traditionally not seen in defamation law as calling your accuser a liar, even though logically that's what it means," said Rod Smolla, dean of the Delaware Law School and a First Amendment scholar.
"But if you go beyond that – if you go from, 'I didn't do it,' to, 'She's a liar,' now you have arguably made a statement of fact" that could be subject to liability, he added.
Trump's status as president does not shield him from civil liability for actions he took prior to assuming office.
In a statement on Tuesday, the attorney defending Trump in the Zervos lawsuit, Marc Kasowitz, said he and Trump's personal lawyer would soon file a response to the lawsuit.
"President Trump continues to deny any allegation of wrongdoing raised in said complaint," he said.
Cosby, 79, who faces allegations of sexual misconduct from approximately 50 women, has also denied any wrongdoing.
Burden of proof
The Cosby and Trump plaintiffs are taking on a tough double burden, experts said.
First, the only way to show the denials by both men are untrue is to prove the incidents took place as described.
"The burden is going to be on her to show that Trump is actually saying something that's false," Clay Calvert, a First Amendment expert at the University of Florida, said of Zervos.
In addition, the women must show Trump and Crosby crossed the line into defamation by deliberately making false statements that seriously harmed the accusers' reputations.
In defamation cases, courts typically examine statements to determine whether they were factual or opinion, as expressing an opinion is generally protected by the First Amendment.
Making that distinction can be challenging. In the Cosby cases, for instance, judges have split on whether the lawsuits should proceed, even coming to opposite conclusions regarding the same statement from his attorney.
U.S. District Judge Mark Mastroianni in Massachusetts rejected Cosby's attempts to have two cases, including Green's lawsuit, thrown out. In his rulings, the judge found that a November 2014 statement from Cosby's lawyer calling the allegations "unsubstantiated, fantastical stories" could be reasonably seen as factual, and therefore potentially defamatory.
By contrast, a Pittsburgh federal judge, Arthur Schwab, tossed a similar case against Cosby, finding that the same statement was "pure opinion" and thus protected.
Unlike Cosby, who has been fairly circumspect in his public statements, Trump has aggressively attacked his accusers, calling the claims "100 percent fabricated and made-up." His rhetoric could make him more vulnerable to a defamation claim, experts said.
Trump has said he never met Zervos at a hotel, despite her allegation that he groped her at a hotel in Beverly Hills, California.
That type of specific fact-based assertion can also make it easier to show defamation if it can be proven false, according to Eugene Volokh, a law professor at the University of California in Los Angeles.
"So much depends on the particular statement and the particular context surrounding that statement," he said.
(Disclosure: NBCUniversal is the producer of "The Apprentice" and also parent of CNBC.)