When officials denied that he was a citizen, Wong Kim Ark took his case to the Supreme Court and won. Today, that decision is the focus of debate over who can be an American.

A third federal judge on Monday blocked President Donald Trump’s executive order ending birthright citizenship for the children of people who are in the U.S. illegally.

Lower courts are following practice and custom, but conservative activists have spent years honing arguments aimed at the specific justices who will ultimately decide.