USMCA/CUSMA has an exit clause. Trump has not exercised that. The treaty is expected to be honoured by both sides during the reevaluation phase. Trump did not do that either. He simply violated the treaty.

As Carney has said, this President's signature is apparently in pencil. If you violate agreements you yourself signed, don't be surprised if people stop trusting you.

Finally, if the current trade deal was so awful... Trump negotiated that. One has to ask, what would it take for you to hold your glorious leader accountable for something he did?