The middle class has been shrinking ever since the 2000s. Some of the middle class was able to reach the upper-income bracket, but most of them fell out of the middle class bracket. Over the past 50 years, the percentage of Americans that qualify as middle class has fallen from 53% to 43%.
See "Middle Class Shrinks Further as More Fall Out Instead of Climbing Up", Dionne Searcey and Robert Gebeloff, The New York Times, January 25, 2015