"These voters aren't motivated by support for their party; they're motivated by opposition against another party."

where is the evidence that people in this movement are able to separate party from the major figures in each party?

a recent podcast (i recall it was 'what could go right') indicated that major media outlets have greatly simplified their pitch (for ratings obviously) to the public by focusing party publicity\policy on an increasingly small number of high profile politicians, thus reinforcing the person=party environment.
e.g., i can envison a more rational world where no one would have ever heard of, or cared about MTG.

its even a bigger stretch to suggest these groups understand differences in policy as a source of their prime motivation.
but i have to concede there is a very small number of seemingly rational people where no explanation, including this one, can be backed up. this group seems too small to make any difference.