That is a very good question that a lamestream media reporter will never ask and a Rat will never answer. They will not answer it because they want to define "middle class" however they want to define it to achieve their aim of being elected to office.
Remember what the Rats and Clinton did back in '93 when they ran everything and rammed their tax increases through? Basically, it ended up being something like everyone earning about $20K a year or more was classified as "the rich" and got gigged for more taxes. The Rats are nothing if not expert practitioners of class envy/warfare. It becomes the have-nots against the have-gots, and the have-gots against the have-got-mores. Just pit everyone against everyone else and when the dust settles the Rats stand at the top of the debris pile.