Is it legal to just rip up treaties without senate?
Probably not , but that hasn’t stopped BO ...the Senate has rendered itself useless and non-existent, so i’m not sure it even matters at this point ...
Nope. But the treaties have provisions for violations by the other side (such as dumping, illegal government subsidies, etc.) and the President typically has the authority to find the misconduct has occurred and impose sanctions of some sort (depends upon the treaty).
The trade agreements such as NAFTA and GATT are not treaties. They were brought into force buy the passage of laws in the usual way.
It's true that people often refer to them as treaties; but they are not.