the Constitution says right there, in black and white, that only Congress can do that.

Well, I found the answer. And just as I suspected Congress fucked up and gave the power away.

Most articles about this are from last year, when he first started this crap, and here's one of the better ones:

https://www.vox.com/2018/3/8/17097206/trump-tariffs-congress

Here's a conservative take on the whole mess:

https://www.nationalreview.com/2018/03/tariffs-congress-handed-president-power-to-levy/

Don't snort because it's National Review-- this article makes sense. If you really can't help gagging at NR, just think of the stopped clock,