The U.S. Constitution empowers Congress to lay imposts and excises. I think that means tariffs.
So how does President Trump obtain authority to increase the tariffs on steel and aluminum?
No one follows the Constitution anymore. It's passe.
Congress, through it's own inability to do anything, conceded such things to the executive branch over time. The Smoot-Hawley Tariff of 1930 was one of the last bricks Congress had to throw before the people took away tariff powers from the corrupted Congress and passed it to FDR.
So, blame democrats. They are usually at fault for most bad things in American history...