It is objective fact that the overwhelming majority of underclass people in the US consider themselves "middle class".
They are very successfully manipulated to vote for people who will deny benefit to people like themselves in the (sincere, induced) belief that it would mean taking from themselves to give to people even lower.
It is the bedrock principle of "conservative" politics, that successfully keeps the upper class from ever needing to pay their fare share. The underclass have been taught to carry them on their shoulders, and like it.
Socially liberal middle class Democrats on the other hand—the would-be saviors of the “underclass”[1]—are convinced that they are voting for the progressive party and not merely the more socially liberal business party which is more interested in maintaining the duopoly than they are in winning against the Rs. No brainwashing going on there.
[1] Half of eligible voters don’t even vote in federal elections. And propensity to vote correlates with socioeconomic class. You say “underclass”. Well, is someone from the underclass more likely to vote R? Or not vote at all?
Sure, the Democratic Party is captured by corporate interests. It is the only way to stay in the game. Lots of sincere people involved would like for it to better represent actual people. But politics is called "the art of the possible" for reasons.
95+% of Americans are underclass. (Between 1945 and ~1975 there was a pretty strong middle class. By 1990 it was gone.) Of those of them who vote, about half vote for each party. The rest, who knows?
They are very successfully manipulated to vote for people who will deny benefit to people like themselves in the (sincere, induced) belief that it would mean taking from themselves to give to people even lower.
It is the bedrock principle of "conservative" politics, that successfully keeps the upper class from ever needing to pay their fare share. The underclass have been taught to carry them on their shoulders, and like it.