As Donald Trump's enemies lick their chops over his unprecedented federal indictment, the former president has quietly scored a legal victory against his estranged niece for breaching his privacy.

New York federal judge Robert Reed found that the former president had cause to sue Mary Trump for publicizing information about his taxes.

"Plaintiff has established, at least at this pre-discovery stage, ‘a substantial basis in law’ for the pursuit of such claim,” the judge wrote.

Trump scores win

This is the second time Reed has ruled against Mary Trump, who previously sued her family for defrauding her out of her inheritance. Reed dismissed the case, saying she had forfeited the right to sue in a 2001 estate settlement following the death of Fred Trump, the father of Donald Trump.

President Trump says his niece violated the settlement by disclosing his taxes to the New York Times, information she also put in her book, Too Much and Never Enough: How My Family Created the World’s Most Dangerous Man. Mary Trump invoked free speech, but the judge was not persuaded.

Trump's lawyer Alina Habba said that Mary Trump was motivated by greed to break the confidentiality agreement.

“Mary Trump had already received a lucrative settlement in the estate proceedings, but she greedily sought to exploit the situation further by disclosing confidential information in violation of an agreement that she freely signed," Habba said.

"She will not be permitted to benefit from her bad-faith conduct, and we eagerly anticipate seeking compensation for the harm caused to my client," she added.

Legal harassment

Like many Trump critics, Mary Trump has been glad to profit off her uncle's notoriety, although, unlike most, she can exploit a family connection.

She is also writing a romance novel with E. Jean Carroll, who claims Donald Trump sexually assaulted her at a department store in the 1990s. A New York court found last month that Trump was liable for battery and defamation against Carroll.

The ruling against Mary Trump came days before her uncle was arraigned on federal charges Tuesday. Trump is accused of mishandling classified documents under the Espionage Act, the law that was used to execute Soviet spies Julius and Ethel Rosenberg.

Trump has slammed the unprecedented indictment as politically motivated election interference orchestrated by his rival Joe Biden.

Trump is also facing criminal charges over "hush money" in New York, and possible charges in Georgia relating to the 2020 election.