Though from some information I have come across, the Tariffs that people are concerned about, is mainly for steel and aluminum imports, which as far as I know our trains don't have any of those metals on them. I am fairly certain they are made out of Die Cast Metal.
The Tariffs at least in my opinion affects things like Appliances and vehicles. So, unless some manufacturer decides to make a model train out of steel or Aluminum. There should be little to no impact on the cost of our hobby. Unless I missed something that mentions that it will increase the price of the our hobby.
I think it is mainly going to affect Big Ticket Items like Heavy Machinery, Vehicles, possibly some equipment used in factories, things like that.