"middle class" is defined but the cohort of wages around the median. By definition, were it to disappear, exactly half the population will be above and half will be below its bounds. It is solely a measure of distribution of wealth not absolute wealth. In recent years more people have risen up out of it. And in many of the past 40 years, more have fallen down out of it. necessarily.

Likewise in the last 40 years, the US per capita GDP has risen close to 70% while the median income has risen less then 20%. But the problem of declining social mobility and rising inequality is not remotely unique to the US.

At least as disturbing is the resultant problem of the steady rise and now mainstreaming of politically extreme views in several western countries in (including the current presidential race obviously). I suggest the economic underpinnings of this problem are issues that we really ought to look at objectively rather than waving the flag and insisting we live in the best of all possible wolds.