Is the House so gerrymandered or would the regional vote swings be so skewed as to allow a Republican majority if the votes were something like 50-47 in favor of the Democrats?

Hypothesis: It's the state-by-state party skew. A party skew is the difference, in percentage points, between a party's shares of votes and seats. Positive skew means a party won more seats with fewer votes. Negative skew means it won fewer seats with more votes. Votes per seat, in other words.

Gerrymandering lets the dominant party pick up a few seats here and there... but districts are small, and our partisan geography is measured on a different scale.

Moreover, states are "gerrymandered" only when they're incorporated. And presidential candidates win them in the same way U.S. Reps win their districts (single-member, winner-take-all). So they let us control for "gerrymandering" when answering the following question: what's America's (presidential) partisanship, regionally speaking?

Here's the 2004 electoral vote:

By now, most have observed the UMICH geographers' 2004 conclusion that population-dense areas tend to be more "Blue." The following is a cartogram of partisanship by county. Counties are drawn in proportion to their share of the nation's population:

Fruits and Votes has crunched some vote-to-seat party skews. (FairVote does this less formally for international elections.) Democrats have faced increasing geographic disadvantage over time. Larger swaths of the U.S. map have come to favor Republicans. Or, in Shugart's words:

Democrats, over time, have gotten a bit less payoff (or decline) in seats from any given gain (or loss) in votes. (Partly this may be a diminishing returns phenomenon, given how dominant the party"s votes majorities were for many years.)...

Every election since 1996 is above the trend. More to the point, in each House election since 1996, the Republican party has won a majority of seats on less than 50% of the vote.

Some possible causes:

1) The "diminishing returns" indicate completion of a partisan realignment,

2) More densely populated areas have grown.

Has it been a partisan realignment? FairVote's work finds America's zones of partisanship have hardened since 1988.

Recent work by Gary Jacobson lends credence to the population density/realignment hypothesis (and touches on relative minority enfranchisement as an additional factor). Republicans win more seats with fewer votes. Democrats win fewer seats with more votes.

With Democrats locked out of the White House and in the minority in Congress, it might seem that there just aren't enough Democratic voters to win elections. But political scientist Gary Jacobson says the problem is actually more complicated: The distribution of Republican voters is more politically effective across the nation.

Jacobson's research shows a little more than half of all the nation's 435 congressional districts over recent decades consistently favored Republican presidential candidates. A little less than 40 percent went for Democrats. (The remainder had a mixed pattern.) Jacobson, at the University of California at San Diego, said this is due to an "inefficient" distribution of Democratic voters, with many concentrations of 60 percent or more in urban areas and places with large numbers of minorities. Republicans, he found, are distributed more evenly, yielding more districts in which GOP voters have a slimmer but sturdy majority.

Factor in the realignment. Jacobson also identifies a decline in split tickets - i.e. Republican voters electing Democratic Reps.

What's so special about regions that doesn't apply to individual districts? Why does the 2004 map look the way it does? The verdict is out. Geographers might say our regional partisanship has something to do with a concept they call "sense of place" - the attitudes connected to home. At any rate, the numbers are in. The closer your neighbor, the less your vote counts.

People with an intuitive sense that this is unfair often blame gerrymandering and the need for independent redistricting. But the problem goes beyond the borders of a congressional district. Given America's hardening regional partisan geography, drawing competitive districts is no small task.

Independent redistricting has not increased competitiveness

Often spotlighted by reformers, Arizona, Washington and Iowa both adopted independent redistricting for congressional and state legislative elections, but these states remain mostly uncompetitive. In Arizona, 15 of 16 U.S. House races have been won by landslide margins of more than 20% since the new plan was drawn, and no incumbent has come close to losing. None of Arizona"s 30 state Senate seats were competitive in 2004, and almost half weren"t even contested. In Iowa, all U.S. House incumbents were re-elected with an average margin of victory of 18%, and 98% of the state"s U.S. House incumbents have won in the decades since adoption of independent redistricting.

Proportional voting could reduce the skews in the House of Representatives and bring back competitive elections - without requiring a constitutional amendment or ending the two-party system.