OK, the fat crybaby from Queens becomes President and gets upset because Mexico looks at him funny, or something. What can he do?
Well, he can cancel NAFTA. It is not 100% clear that doing so will immediately cause tariffs to snap back. It is also possible that Mexico will regain its GSP preferences. The NAFTA Act of 1993 is silent on cancelling the agreement. But Fat Crybaby can do what he wants until a court decides. So boom, Mexico!
(Section 2 of the NAFTA Act implies that ... well, go read it and tell me. Canadians in particular.)
But that just hits them with America’s low existing tariffs. Fat Crybaby, he’s a mean mofo from Jamaica Estates. Gangsta lean straight from Queens, except whiny. So what else can he do without going full Mussolini? Well, step one is Section 122 of the Trade Act of 1974. Wham! 15% tariff surcharge plus quotas as tight as President Fat Crybaby wants to make them. (Presumably, tight enough to raise import prices 45%.)
Could he go further? Sure! President Nixon did in 1971. Now, the Customs Court found against him, but keep two things in mind. First, we do not know how higher courts would have ruled. Second, Nixon imposed the tariff surcharge on August 15, 1971. The court ruled on July 8, 1974. That is a long time.
But if gets better! Section 338 of the Tariff Act of 1930 allows retaliatory tariffs of up to 50%! Badabing! Now, in point of fact, Section 338 is aimed at tariff jurisdictions that discriminate against the United States compared to other countries. But hey, see above about how long it will take for legal challenges to say that the authority does not apply to target to be decided.
And should President Fat Crybaby decide that China is the target, well, the International Trade Commission has already issued a finding under Section 337 of the same law. Whammo! In the nose!
And then there is the Emergency Economic Powers Act of 1977. It involves foreign exchange transactions, but it could be used to effectively impose quotas. So if a court ruled against the above, Fat Crybaby could pull out Section 203 of the Economic Powers Act and wait for the courts to decide that one.
In short, if Fat Crybaby throws a temper tantrum in office, then he can pretty much do whatever he wants, at least for several years. Sure, the WTO will rule, but whatever. Winning!