While the long stagnant periods in wages (Noah marks the one from the mid 1970s to mid 1990s, but ignores the one from 2001 through about 2012, perhaps because he realizes that marking most of the last 50 years, accurately, as periods of wage stagnation, rather than falsely claiming that that ended in the 1990s, would undermine the rosy picture he is painting) are a problem, the distributional dynamics are probably the thing most closely associated with the perception of a hollowed out middle class.
Also because they were doing well, compared to past experience, relative to those higher on the income distribution.
That is, inequality narrowed throughout the post-war era until around 1980, when it turned around and shot up.
https://fred.stlouisfed.org/series/SIPOVGINIUSA
While the long stagnant periods in wages (Noah marks the one from the mid 1970s to mid 1990s, but ignores the one from 2001 through about 2012, perhaps because he realizes that marking most of the last 50 years, accurately, as periods of wage stagnation, rather than falsely claiming that that ended in the 1990s, would undermine the rosy picture he is painting) are a problem, the distributional dynamics are probably the thing most closely associated with the perception of a hollowed out middle class.