At the heart of the legal debate over President Donald Trump’s executive order on birthright citizenship is the interpretation of the 14th Amendment’s citizenship clause. While there are numerous practical hurdles to eliminating birthright citizenship as it’s been practiced, the president is on solid legal footing. The clause (“All persons born or naturalized in the United States, and subject to the jurisdiction thereof”) should not be interpreted as conferring automatic citizenship to children born of illegal immigrants. Setting aside constitutional interpretation, that just seems like common sense.

But not everyone sees it this way, hence the controversy. According to two federal judges who have issued injunctions since the order was issued, the language of the clause should be read at its broadest, which would grant citizenship to any person born within the territorial boundaries of the U.S., regardless of the status of the parents. Proponents of this interpretation point to the Supreme Court case United States v. Wong Kim Ark (1898) in which the court held that a child born within the territorial boundaries of the U.S. to temporary Chinese immigrants was a citizen.