The New York court refused to overturn the decision to pay porn star Stormy Daniels $130,000 for silence in the Trump case.
The judge found Trump's actions personal rather than official, so immunity does not apply.
In a 41-page ruling released Monday, Judge Juan Merzhan sided with the office of Manhattan District Attorney Alvin Bragg, which brought the case. Prosecutors have argued that the case involves Trump's conduct, not his official actions as president.