Trump Loses Case to Enforce Omarosa Manigault Newman’s N.D.A.

“The statements do not disclose hard data such as internal polling results or donor financial information,” Mr. Brown wrote. “Rather, they are for the most part simply expressions of unflattering opinions, which are deemed ‘confidential information’ based solely upon the designation of Mr. Trump. This is exactly the kind of indefiniteness which New York courts do not allow to form the terms of a binding contract.”

At another point, Mr. Brown wrote that the agreement “effectively imposes on Respondent an obligation to never say anything remotely critical of Mr. Trump, his family or his or his family members’ businesses for the rest of her life.”

The arbitrator added, “Such a burden is certainly unreasonable.”

Mr. Phillips, who is based in Florida, said the lawsuit had been an abuse of power by a sitting president. “It’s over,” he said. “We’ve won in Donald Trump and the Trump campaign’s chosen forum.”

Arbitration decisions do not create a precedent, according to Shira A. Scheindlin, a retired Federal District Court judge for the Southern District of New York. That means that there is no potential impact from the Manigault Newman case on ones filed against other Trump employees.

However, a ruling in one case “may be persuasive” in another, said Cliff Palefsky, a lawyer in San Francisco who is an expert in the arbitration process. In the decision in Ms. Manigault Newman’s case, the arbitrator referred to a ruling in a class-action suit filed in New York by a former Trump campaign aide, Jessica Denson. In that case, a judge ruled that the Trump campaign’s nondisclosure agreements were not enforceable.

Charles Harder, the defamation lawyer who had represented the Trumps over the years and who was handling Ms. Manigault Newman’s arbitration case, parted ways with the Trumps before the decision was issued.

The decision cannot be appealed, other than on the basis of fraud alleged against the arbitrator who heard the case. That leaves Mr. Trump with little recourse for continuing to pursue an action against his former aide.