There are more than a few mechanisms to impose tariffs to level the playing field. Where this gets incredibly dumb is:
1. He's trying to use national security as the reason for these tariffs. Those WTO rules regard things like, y'know, military arms and supplies. They're undoubtedly going to get dunked on if they try to actually argue that.
2. These tariffs were presented to him by advisors that would have leveled the playing field. Trump then opted to double that recommendation since he was in a bad mood.
3. He is still threatening to impose these tariffs on Canada and Mexico, who will respond in kind like most of the world has threatened since he announced this. This becomes an obvious issue when you realize that this will disproportionately negatively impact the Rust Belt.
4. It will still be cheaper for corporations to outsource labor and export goods to the United States.
5. This will cause prices to rise on a host of goods.
6. Trump is considered a joke in the business world since he's actually a terrible negotiator. He doesn't negotiate prices when he licenses his brand out to anyone who asks and is part of the reason of why he can't take out loans anymore. It's why the producers of The Apprentice went after him to host the show since they thought it would be hilarious if they made a notoriously bad businessman the face of a business oriented show.