What are some key NAFTA problems USMC solves?

NAFTA survived almost intact as the changes made are mostly hot air from Trump and any modifications to the agreement must go for approval by the respective Congress of each country. The underlying reason for the agreement to stand mostly as is arises from the fact that manufactures are dependent on the supply chains they established during the years of the agreement and a sudden cancellation would have brought disastrous economic consequences to all three countries. Disrupt, demolish and then take credit for appeasement or building is the current logo over the Trump's Whitehouse.

Discussions between the United States and Canada had turn sour amid insults from Trump to PM Trudeau. The president said he had rejected a meeting with Mr. Trudeau because he would no buckle under Trump’s “charm”. However, the office of PM Trudeau said no such meeting had ever been requested. Trump also threatened to tax auto exports from Canada to the United States if Canada did not agree to his demands.

In essence the changes trumpeted by Trump are merely text editing and spell check of the entire document but Trump like to take credit for someone else’s work as when he waves to his crowd of supporters with a hat that doesn’t belong to him. In any case, modifications to the agreement must be reviewed by a new Congress expected to be dominated by the democrats who will probably be impeaching Trump if director Mueller’s report is as damming as expected.