President Trump’s forthcoming plan to end birthright citizenship for the children of illegal aliens and foreign tourists by clarifying what it means to be “subject to the jurisdiction” of the United States at birth would reverse the yearslong federal agency practice of granting citizenship to the U.S.-born babies of these groups.

Although the question of whether one’s mere presence, as opposed to some deeper connection, entitles one’s U.S.-born child to automatic citizenship has been a hot one for decades, the debate is far younger than the actual Citizenship Clause of the 14th Amendment. This is itself telling, says constitutional law professor John Eastman, who has dug deeply on this issue.