Every 10 years, it's time for reapportionment and redistricting. The framers of the Constitution created the first regularly scheduled national census and required, for the first time that I am aware, that representation in a legislature be apportioned according to population.
Reapportionment is automatic: A statutory formula takes the Census figures and apportions the 435 House districts among the 50 states. Wyoming and six other states will each get one, California will probably get 53, and the rest some number in between.
Seven states, according to projections by Polidata Inc., will gain a House seat, and Texas will gain four -- nine states will lose a House seat, and Ohio will lose two. Overall, states carried by John McCain in 2008 will gain a net seven seats (and electoral votes), and states carried by Barack Obama will lose seven.
But that doesn't necessarily mean Republicans will gain House seats. That depends on redistricting -- how the lines are drawn by the politicians in each state (or, in a couple of cases, by nonpartisan commissions).
That's particularly true in states with large numbers of districts and densely packed metropolitan areas. You can't do much gerrymandering in a state with only a few districts. But you can in states with more than four or five.
Eighteen months ago, it looked like Democrats were going to profit from redistricting. An optimistic scenario for Democrats, extrapolating from the 2008 election results, was that if they could gain three governorships and three state senates and otherwise hold what they had, they would control redistricting in 14 states with more than five districts, including California, New York, Illinois, Michigan, North Carolina and New Jersey.
Those states are projected to have 195 districts in the House elected in 2012. Clever redistricting could move between one and two dozen into the Democratic column. That would have been the Democrats' best redistricting cycle since the one following the 1980 Census.
But that scenario now is the stuff of dreams. Democrats are threatened with losing many governorships and legislative chambers, and their chances of taking over many from the Republicans look dismal.
Instead, the optimistic scenario belongs to the Republicans. If they hold what they have and capture a few governorships (Ohio, Tennessee, Wisconsin) and a few legislative chambers (the Houses in Indiana, Michigan, Ohio and Pennsylvania, and both houses in Wisconsin), they will control redistricting in 11 states with more than five House seats, including Florida, Georgia, Michigan, Ohio, Pennsylvania and Texas. Those states are projected to have 178 House seats.
This would be an even better redistricting cycle for Republicans than the one following the 2000 Census, which was their best in 50 years. It could move one to two dozen House seats into the Republican column.
But a few caveats are in order.
First, optimistic scenarios don't always come true. If Republican Meg Whitman is not elected governor in California, Democrats will be able to draw the lines of its 53 districts. That could offset Republican gains elsewhere. And it's not a sure thing that Republicans will make the gains they need to control the process in several states.
Second, redistricting doesn't lock up seats for one party forever. A few years ago pundits were lamenting that it did -- and then Democrats won dozens of seemingly safe Republican seats in 2006 and 2008. This year, Republicans may win many seemingly safe Democratic seats.
The last redistricting cycle came during a period of stable partisan alignments that persisted from 1995 to 2005. Redistricters could pretty well count on voters voting the same way they had last time and the time before.
Now we seem to be in a period of very unstable partisan alignments. What looks like a safe seat based on 2008 numbers may not look safe under 2010 numbers. And those numbers may not be etched in stone. No one I know is predicting confidently how Americans will vote in 2012.
In the end, the voters get a say. But in an otherwise close election, redistricting can determine control of the House. And that can make an enormous difference in legislative outcomes, as it has during the past decade.
The unpopularity of the Obama Democrats' policies seems sure to hurt the party this year. Redistricting seems likely to extend the pain for several more election cycles.