Even before her bombshell decision on Monday to dismiss former President Donald J. Trump’s classified documents case, Judge Aileen M. Cannon had made any number of unorthodox rulings.

In fact, since Judge Cannon took control of the case in June 2023, many of her decisions have been so outside the norm that they have fueled intense criticism of her legal acumen, stoked questions about favoritism toward Mr. Trump and slowed the documents case sufficiently that it would not come to trial before Election Day.

Still, almost no one, including some defense lawyers working on the case, expected Judge Cannon to throw out the charges against Mr. Trump by ruling that Jack Smith, the special counsel who filed the indictment, had been unconstitutionally appointed to his job — especially on the first day of the Republican National Convention.

The ruling upended 25 years of Justice Department procedure for naming and governing special counsels and called into question decisions by previous courts reaching back to the Watergate era.

“The very definition of an activist judge, she has single-handedly upended three decades of established law historically used fairly and in a bipartisan manner,” said Joëlle Anne Moreno, a law professor at Florida International University.

From the moment that Judge Cannon was assigned to the case, there were questions about her ability to handle it. She took control of one of the most significant prosecutions in American history, rife with legal and political complexities, even though she had been a judge for less than four years and had extremely limited experience in overseeing criminal trials.