Steve Rose is one of our finest labor economists and he does some very innovative data work. Below is a chart from a new issue brief of his coming out from the Urban Institute on the growth of the upper middle class, updating an earlier paper of his with new data.
The chart shows the growth of the upper middle class, defined as a family of three-equivalent income that is 5 to 17.5 times the federal poverty line for a family of three (read this brief and his earlier one for an explanation of this methodology, which I believe is sound). In today's terms, that is roughly $100,000-$350,000. The growth is impressive, going from 13 to 37 percent of families between 1979 and 2019.
The chart also shows the lower middle class and poor/near poor declining from 48 to 29 percent over the same period. The middle middle class also declines though more modestly, going from 39 to 31 percent. The distributional changes clearly show that the middle middle is declining not because such families are shifting downward but rather because they're going upward into the upper middle class.
Elsewhere in his brief Rose reports that, at this point, not only are 57 percent of white families upper middle class (or rich) and 59 percent of Asian families but also 40 percent of black families, which may surprise. Hispanics are significantly lower at 28 percent.
If you don't think the growth of the mass upper middle class has implications for politics, you haven't been following the evolution of the Democratic party. It's not hard to see how this fits into the story about the rise of the Brahmin left.