The numbers being used here feel pretty contrived to me, like the article has decided its conclusion and is going to find things to support it. Especially given

The numbers being used here feel pretty contrived to me, like the article has decided its conclusion and is going to find things to support it. Especially given the pseudo-title in the URL ("americas-middle-class-is-shrinking-yet-thriving-in-many-other-european-countries") which is certainly not borne out by the final graph which depicts the proportion of middle-income adults falling in the US, but by less than Luxembourg, Finland, Germany or Spain. In general it looks like the US has a wider-spread income distribution, but over time there's a trend to most of these countries spreading wider as well, which drives the reducing size of the middle income bracket. The exceptions to that reducing size look pretty heavily correlated with increased average income (Denmark, the Netherlands, France, Ireland and the UK). That suggests to me that the original question ("What’s going on with America’s middle class?") is poorly framed to begin with; this doesn't back up the assertion that there is anything especially unusual going on with America's middle class, it appears to be more or less the same thing happening in many other countries.