An extraordinary legal showdown took place last weekend over President Donald Trump’s invocation of an 18th century wartime act to deport hundreds of immigrants to a prison in El Salvador.

The president’s invocation of the wartime law enacted in 1798 was quickly blocked by a federal judge. It had only been used three times before in U.S. history.

In a 226-year span, the Alien Enemies Act of 1798 had been invoked only three times — until now. President Donald Trump fulfilled a campaign promise to use the wartime act as a shortcut to deport suspected members of a Venezuelan gang, according to an executive order signed March 15.