The biggest problem is that this move further marginalizes the United States, pisses off our allies and trade partners, and makes it more difficult to negotiate from a place of mutual benefit. Trump is clearly demanding "better deals" for America - why should other countries work with us?
We have a lot of money & resources, but the other 194 nations on Earth could get by without us just fine if Trump is going to behave like a greedy child. The more they realize that, the less they're going to be willing to work with us.
Trump will not get a "better deal," he'll get doors slammed in his face. This isn't Trump the Great Negotiator, this is
Trump the
Guy Who Reneges on
Contracts with
Regular Americans.