Part of this mystery isn't one at all: the economy simply isn't as healthy as the headline numbers suggest. Unemployment has fallen, in part, because so many people have given up looking for work rather than finding it, and there are still millions of part-timers who want full-time jobs.
But then there are deeper factors at work. The economy has gotten bigger, but much of that growth hasn't reached the middle class. Indeed, the top 1 percent grabbed 95 percent of all the gains during the recovery's first three years. And that's not even the most depressing part. Even adjusted for household size, real median incomes haven't increased at all since 1999. That's right: the middle class hasn't gotten a raise in 15 years.
But one of the biggest, and least appreciated reasons Democrats might be struggling, is that the middle class is poorer, too. Median net worth is actually lower, adjusted for inflation, than it was in 1989. Even worse, it's kept falling during the recovery.
Yes, even after the economy started to grow again, and the stock market started to boom, and housing prices began to bounce back, the median net worth of the average American household continued to decline.