(1) you're lying, it's only upper-middle class people who support Trump. It's all lies!
Literally no one anywhere has espoused this view, because it's disproven by about a five-second Google image search of a Trump rally.
... and so on. Basically either downplay or dismiss anything the supporters of the other side care about. Then wonder why they aren't listening ...
Again, another bullshit strawman. Plenty of folks on the Left (myself included) understand why a lot of working-class people would support Trump. What infuriates us is that their support is built on a foundation of industrial-strength bullshit arguments and outright lies (it's all Mexico's fault! We're gonna bring back manufacturing and coal jobs! Liberals hate America! Obama is a Kenyan Muslim! etc. ad nauseum).
And those same people seem impervious to fact and cogent argument that no, in fact, that's not true. It's exceedingly difficult to stay engaged and sympathetic to someone who doubles-down on their own ignorance and tops it off with in-your-face belligerent pride in their own ignorance.
However, the problem with working out why working-class people aren't acting "like they're supposed to" in the "theory" is that the working person isn't using your theory to decided for themselves how the world works. To them, the categories and conflicts fall on completely different lines, so if you still couch things in the traditional labor vs capital framework, you might as well be speaking a foreign language.
Now, there is some truth to that. Which is to say, it's ethno-nationalist populism masquerading as economic populism. Sanders is an economic populist, which at its root, is what a lot of those working-class white Trump voters are really seeking. Trump (or more properly, the miasma of people surrounding him) are ethnonationalist populists exploiting both the sense of being left behind by globalism and capitalism, and the sense of being left behind by fairly sweeping generational changes in attitudes on social issues like gender rights, sexuality, abortion, etc. People who weren't culture warriors in the 80s and 90s, but now they're a little weirded out by things like transgender rights, SJWs, etc.