This is an excerpt from Executive Insight Briefing, produced every Thursday by the National Journal’s Daily Briefings Team.

The middle class, according to a Pew Research Center study released on Wednesday, over the past decade has grown smaller, less affluent, and less optimistic. Eighty-five percent of adults who describe themselves as middle class say it is more difficult to preserve their standard of living now than it was 10 years ago, according to the survey.

For the first time since the end of World War II, mean family incomes across all income tiers declined over a decade. Middle-tier median household income fell, for three-person households, from $72,956 in 2001 to $69,487 in 2010. Perhaps more ominously, median net worth sat at $93,150 in 2010, a meager increase of just over $2,000 from 1983.

That the middle class has been hollowed out is not news; decades of social and economic changes have fueled that trend. But the numbers lay out starkly the challenges for politicians to appeal to the largest swath of voters. Of the large majority who believe that maintaining their lifestyle has grown more difficult, 62 percent ascribe “a lot” of the blame to Congress, 54 percent blame banks and financial institutions, and 47 percent finger large corporations.

Of the two presidents who were in office over the decade of decline, President George W. Bush receives 44 percent of the blame and President Obama 34 percent.