What explains the anti-establishment sentiment?

After last night's election results, there's no doubt that the electorate has contempt for Washington incumbents and the political establishment.  Virtually every media account dutifully recites the same storyline -- that these results reflect an "anti-incumbent" mood -- but virtually none of these stories examines the reasons for that "mood."  Why do Americans, seemingly regardless of party affiliation or geographic location, despise the political establishment?

One reason why media...