A U.S. judge on Saturday declared President Donald Trump's firing of the head of a federal watchdog agency illegal in an early test of the scope of presidential power likely to be decided at the U.S.

U.S. District Judge Amy Berman Jackson ruled on Saturday that Office of Special Counsel head Hampton Dellinger can remain in his role after President Donald Trump tried to terminate him without clear cause.

The federal judge’s decision blocks Trump from removing Hampton Dellinger as head of the Office of Special Counsel and sets up a likely Supreme Court battle over the president’s powers.