But the law also insists on Hispanic-majority districts, although few Hispanics have ancestors subject to discrimination in this country and although many are non-citizens ineligible to vote. In Texas, where Hispanics are less Democratic than elsewhere, Republican redistricters adjusted by creating several elongated districts linking Hispanic-majority areas with heavily Republican counties.
All these results tend to refute some conventional wisdom about redistricting.
It is said that partisan redistricting can swing dozens of seats the way of one party through the creation of grotesquely shaped districts. But most grotesque districts in the current cycle owe their shape to the Voting Rights Act. Otherwise partisan districting has produced pretty clean lines.
A few years ago, many lamented that crafty redistricters could prevent serious competition and lock in party control. But that's only true when political alignments are static, as they were between 1996 and 2004.
When voters change their minds, redistricters can turn out to be too clever by half. Many districts designed to elect Republicans elected Democrats in 2006 and 2008. Many districts designed to elect Democrats elected Republicans in 2010.
The less aggressive redistricting plans adopted this cycle show that even strong partisans have absorbed the lesson that if you create a bunch of 53 percent districts you can lose them when your side's support goes down by 4 or 5 percent.
In addition, patterns of support can and usually do change at some point in the 10-year interval between censuses, as issue focus changes and presidents and presidential candidates give parties different images. Democratic areas can become marginal or even Republican, while some marginal areas can trend toward Democrats; and vice versa.
Currently the realclearpolitics.com average of recent polls shows a 44 to 44 percent tie between the parties on the generic ballot ("which party's candidate for the House would you vote for?"). That question has underpredicted Republican performance in the election in the past, though not in 2010.
But assuming the popular vote is evenly split, Republicans are likely to retain their House majority -- primarily because the Voting Rights Act packs too many Democrats into too few districts. Redistricting turns out to matter less than we thought.