Well, that and it increasing the cost of steel, which will increase the cost of their products and reduce their sales - regardless of who they buy the steel from.
That said, if tariffs are used tactically, and the diplomacy is good, brief tariffs can help in the long run. In the short term - or however long the tariffs last - its like giving a tax break to one guy and raising the cost to everyone else.
The mental midgets we lovingly call Free Traitors are some of the stupidest people on earth.