one detail is that when dealing with a trading partner that is 10x smaller than you, is that you have so much leverage that you can come up with any terms and the other party has really no choice but to accept them...
Mexico exports:
30-40% tariff or whatever he is proposing is probably a bit ridiculous though, it would shake up global economy a bit and results would be quite unpredictable... but little harm in using that as a threat to gain a leverage in some deal...