The U.S. government's unprecedented use of National Guard troops in Los Angeles to protect officers carrying out President Donald Trump's immigration crackdown was illegal and should be ended, a lawyer for the state of California told a federal judge on Tuesday.

The three-day non-jury trial before San Francisco-based U.S. District Judge Charles Breyer will determine whether the government violated a 19th-century law that bars the military from civil law enforcement when Trump deployed the troops in June, as the state of California claims in its legal challenge.

Lawyers for President Trump and Gov. Gavin Newsom faced off over the National Guard deployment in Los Angeles — and debated whether they were subject to a "constitutional exception.