A growing middle class, presented a poltical danger to the interests of the wealthy, it's growth took away from their status and privilege, so it had to be both shrunk and turned against the the lower class.
Nixon started it, Reagan perfected it with anti-union laws, demonizing the poor, slashing pensions, underfunding education and loosing the taxes and regulations on corporations.
Classism, Sexism, Racism and Religion are all used to further seperate working class Americans, who have more in common than not, and to give them someone to focus their anger and blame on, when their own upward mobility stalls; all the while the rich get richer.