Gerrymandering

The national vote for Democratic congressmen was 51%, vs. 49% for the GOP, essentially matching the Obama-Romney outcome. But the new Congress has only one or two fewer GOP seats than the last one, and they still have a substantial majority. That's the result of the clever redistricting done by GOP-controlled legislatures in 2000 and 2010. (And some off-cycle shenanigans in Texas, if I remember right.)

This figure shows just how well that worked. The blue and red bars are histograms of the district level votes, blue for Dem & red for GOP, natch, showing the fraction of districts with given vote margin, grouped by 5% bins. The GOP peaks at center right are in the 55-60% and 60-65% ranges, where they crafted districts of safe but not concentrated seats. The buckets at 65% and higher are all strongly blue dominated - those are the districts set up to hold the resulting "excess" of Dem. voters.

There's only one way to fix this (short of armed insurrection). Get Democratic control of more state legislatures (difficult because of the gerrymandering) and governorships (less difficult because those are statewide offices). Then turn the tables.