This truly is a complicated issue, and I would never claim to be an expert in this area. However, some common sense results of raising Tariffs on items imported from Mexico would have an adverse result as well. The first would be the rise in cost of said items both at the Wholesale and Retail level. That rise in cost would be passed directly on to the American Consumer, which would result in a decline in "buying power" by the American Consumer.
Raising Tariffs on Mexico does not guarantee that the American Consumer would immediately begin to "buy American." Thus, it is reasonable to believe that "demand" would drop for certain items........and when "demand" drops, the need to produce the items would also drop which would directly result in a drop in Employees who produce, ship, house, and stock/sell the items. As well, when prices increase, so does Inflation. The Cost of Living is surely a serious problem for the American Consumer. Increases in the Cost of Living could cause our Country to enter a Recession, as the American Consumer could not afford to purchase the necessities and/or amenities.
Items produced in Mexico and imported into the U.S. also create jobs here in the U.S. It is a complicated issue, and in my opinion, rushing to action would be a dangerous thing. Serious minds need to spend serious time considering ALL of the various factors/results of any action taken to dismantle NAFTA I would think.
I'm pretty sure that the US will uphold the terms of NAFTA with Canada since we are more or less economic equals.
Where NAFTA hurts both the US and Canada is that it removed a lot of import tariffs for products coming out of Mexico which is not an economic equal thus making it possible for Mexico to not only produce products more cheaply due to less government regulation in that country and considerably lower wages but now neither the US or Canada can level the playing field with import tariffs.
I think the US got hurt more by NAFTA than Canada did (I could be wrong) because Canada hasn't been bleeding jobs into Mexico but the US has.