For the last few weeks, there has been ongoing litigation over President Trump's effort to use the Alien Enemies Act of 1798 as a tool for mass deportation. The AEA allows detention and deportation of foreign citizens of relevant states (including legal immigrants, as well as illegal ones) "[w]henever there is a declared war between the United States and any foreign nation or government, or any invasion or predatory incursion is perpetrated, attempted, or threatened against the territory of the United States by any foreign nation or government." Four federal judges - three district courts and Judge Henderson of the DC Circuit - have ruled that Trump's invocation of the AEA is illegal because there is no declared war, and the activities of the Venezuelan drug gang Tren de Aragua (which Trump cites as justification for using the AEA) do not qualify as an "invasion" or "predatory incursion."
