I've been perplexed for a while how Republicans do so poorly on California redistricting plans that people draw up using Dave's App. After all, Republicans hold only 36% of the congressional seats now. If you only include Republican and Democratic vote totals, Republicans have never been beaten 64%-36% in a statewide California election.
All of these calculations use Obama-McCain numbers to judge how competitive a congressional district is. Those numbers don't tell us the truth.
Barack Obama won California 62%-38%. If you look at the 16 statewide elections in 2006 and 2010, Obama beats the Democrat in 15 of them. Even at their best Obama outpaced California Democratic candidates by 2-12 points. Unfortunately California held no statewide elections in 2008, so we can't compare apples to apples. With 16 elections before and after the Obama election we have a good sample how candidates will do statewide. "Aha," you say. "But Barack Obama was an exceptional candidate." Exactly. And he won't be running for California statewide or congressional office. Yet we look at his numbers when judging how congressional candidates will do. The Democrats only have one Barack Obama. Other candidates don't generate that excitement.
So let's look at how congressmen did.
This group of Democratic congressmen are in majority-minority districts. These are overwhelmingly Democratic. Due to the Voting Rights Act rules, there likely will be a similar amount of these districts in 2012. Since they'll have the same proportion of Blacks and Hispanics as these districts do, we'll likely be able to set aside those voters for these districts. They won't impact the remaining 33 districts very much.
Here are 14 White Majority Democratic districts. Republicans did a lot better in House, Senate, and Gubernatorial races in 2010 compared to Barack Obama in 2008. Despite having strong incumbents and often having weak challengers these congressmen didn't do much better in 2008 and 2006 than Obama did.
Republican congressmen outperformed John McCain in 50 of the 52 contested congressional elections from 2006-2010. This includes a Republican year and two Democratic years, Republicans with strong challengers and weak ones, and 3 open seats. (highlighted in pink) At their worst, Republican congressmen outperformed John McCain by 12 points. At their best they were 21 points better. If you average the seats that'll be contested in 2012, the range was 4-12 points more Republican.
If the McCain numbers were reflective Republicans would win 16 seats in an average year. If you add 4 points to each Republican, you'll get Republicans ending up with 23-24 congressmen in an average year. Based on Republican share of the vote in California that's about what you'd expect. If you add 2 points to each Republican, they'd get 18-19 congressmen in an average year. About what they have now.
It's possible that an open seat will be close to McCain but incumbent Republican congressmen will outperform him, in most cases by 12 or more points. If Barack Obama wins a district 51-49, an incumbent Republican will likely do at least 55%-45%. And incumbent Republicans will be running in 2012.
Thus, any evaluation you read based on John McCain's vote total will be biased to the Democrats.