Alec MacGillis for NYT Sunday Review:

Liberals have a simple explanation for this state of affairs: Republican-led gerrymandering, which has put Democrats at a disadvantage in the House and in many state legislatures. But this overlooks an even bigger problem for their party. Democrats today are sorting themselves into geographic clusters where many of their votes have been rendered all but superfluous, especially in elections for the Senate, House and state government.

This has long been a problem for the party, but it has grown worse in recent years. The clustering has economic and demographic roots, but also a basic cultural element: Democrats just don’t want to live where they’d need to live to turn more of the map blue.