US judge holds Trump in contempt over civil fraud probe
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James is pursuing a civil probe into the ex-president and the Trump Organization.
She said in January that her probe had found that the Trump Organization fraudulently overvalued multiple assets to secure loans and then undervalued them to minimize taxes.
James successfully argued that Trump was in violation of a court order to produce the accounting and tax documents to her investigators by March 31.
She declared the ruling a "major victory."
"For years, Donald Trump has tried to evade the law and stop our lawful investigation into him and his company's financial dealings. Today's ruling makes clear: No one is above the law," she said in a statement.
James can sue the Trump Organization for damages over any alleged financial misconduct but cannot file criminal charges.
The Trumps have claimed that James, who was elected to her position and is a member of the Democratic Party, is running a politically motivated probe.
Alina Habba, a lawyer for Trump, said she would appeal Monday's ruling.
"All documents responsive to the subpoena were produced to the attorney general months ago.
"This does not even come close to meeting the standard on a motion for contempt," she said in a statement emailed to AFP.
Trump and his family have repeatedly tried to shut down James's investigation.
In February, he and his children Don Jr and Ivanka were ordered by a judge to submit to questioning under oath. That order is under appeal.
James's probe is one of several legal battles in which the 75-year-old is embroiled, threatening to complicate any bid for another run for the White House in 2024.
The Trump Organization is also under investigation by the Manhattan District Attorney for possible financial crimes and insurance fraud.
Last July, the Trump Organization and its long-serving finance chief, Allen Weisselberg, pleaded not guilty in a New York court to 15 felony fraud and tax evasion charges.
His trial is due to begin in the middle of this year.
Trump has so far kept Americans guessing about whether he intends to seek the Republican nomination again.