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.

Trump first referenced the act during his inauguration, promising to "eliminate the presence of all foreign gangs and criminal networks" in the U.S.