I suspect most of us on HN are a bit optimistic about the definition of middle class. Maybe we identify socially as middle class. But unless the numbers are lying, a huge chunk of America is in a much tighter financial situation.
In classical analysis of capitalist economies (starting with, but not limited to, the socialist critics that first identified “capitalism” as a thing) the “middle class” isn't middle in the sense of including the median person, but in being between the capitalist class (that derives support through applying rented labor to capital they control) and the working class (which derives support through labor rents from capitalists), and includes people whose support comes from a mixture of capital and labor, most typically the yeoman farmer or independent tradesman who primarily applies his own labor to his own capital.