This is reductive. Even PhD economists are crap at predicting effects of certain policies (see the Federal Reserve - it has thousands of them!). The economy is very complex to model (and has reflexivity), and generally you will find credentialed experts on both sides of anything short of a trivial debate.

Tariffs have pros/cons, as does any other policy proposed by the two candidates. And the most tricky thing when computing the effects of these policies is: "what is the quantity we're trying to optimize for?" - where the "welfare of the people" is not really a measurable thing.