What is the Alien Enemies Act of 1798 and how is Trump using it?

President Trump's use of the Alien Enemies Act of 1798​ to deport alleged Venezuelan gang members kicked off a legal battle.​

What is the Alien Enemies Act of 1798 and how is Trump using it?
President Trump's use of the Alien Enemies Act of 1798​ to deport alleged Venezuelan gang members kicked off a legal battle.​