There are, as usual, many causal or root layers to each Trumpish issue.  In this example (to be simplistic), at the highest level is some question on whether the USA can or must benefit from free-ish trade or at another level, whether the USA has any vested interest in trade when it can pretty well make anything it wants domestically (more or less) and if so, under what set of circumstances.... And the answers to these higher-general-principle issues lead to more detailed or adjacent ones like, if you are going to trade does that have any relationship to your other foreign policy priorities and does that in turn relate to how much you can afford to pay (literally) to "buy American" as an absolute and then when you answer that and find that you probably cannot pay for regressive trade practices AND all the other things you have promised or conceived, how much of the protectionism can you afford and with respect to what and so on.

Dairy and softwood are non-issues in all of this.