|Cross posted at Swing State Project and Daily Kos.
How do various factors affect a House candidate's percentage of vote in the election? All the following numbers relate to average effects. Individual results may vary.
The first four are the variables used to predict the expected performance:
1. High D/R Fundraising Ratio: +15 points (about 5 points for every factor of 3 increase)
On average, challengers running for a seat currently held by the opposite party will gain 15 points if they outraise their opponent by a factor of three compared to if they raise only one tenth of their opponent's money, if all other factors are equal. Note that the D/R Fundraising Ratio is fairly closely correlated to absolute amount of money raised by the challenger, so we can also say that challengers will greatly improve their performance if they raise a great deal of money, regardless of the incumbent's fundraising.
2. Running as incumbent party: +10 points
Candidates running for a seat currently held by their own party (incumbents or open seat candidates) will gain, on average, 10 points compared to if they were running for a seat currently held by the opposite party, if all other factors (including D/R Fundraising Ratio) are the same.
3. Running in a more favorable district: +10 points (1 point for every 3 point change in Bush's vote in the district)
Democrats running in the most liberal Republican-held districts (Bush vote 40-45%) will gain 10 points compared to Democrats running in the most conservative Republican-held districts (Bush vote 65-75%), if all other factors (including D/R Fundraising Ratio) are the same. Democrats running in the moderately liberal Democratic-held districts (Bush vote 30-35%) will gain about 10 points compared to those running in the most conservative Democratic-held districts (Bush vote 60-65%).
4. Political climate: +6 points
On average, Democratic challengers did 6 points better against Republican incumbents in 2006 compared to 2002 (4 points better than 2004) when accounting for D/R Fundraising Ratio and district partisan makeup. Republican challengers did 4 points worse in 2006 compared to 2002. In other words, Republican money was worth less in 2006 than in 2004 or 2002. They had to raise more relative to their Democratic opponent to get the same result.
The following comparisons are made by comparing actual performance to calculated performance, accounting for the four factors above: D/R Fundraising Ratio, district composition, incumbent party, and political climate. The numbers given are average residuals of the regressions.
5. Raising more than $2 million as a challenger: +3 points
Remember, this is after accounting for D/R Fundraising Ratio. If both candidates raise the same amount of money, dollar-for-dollar, then the more money a challenger raises, the better the challenger does. A challenger who raises more than $2 million (and whose opponent also raises more than $2 million) increases performance by about 3 points compared to one who only raises $100,000 (and whose opponent also raises only $100,000). In other words, high-spending races with fundraising parity are generally to the advantage of the challenger. (This leads to the strange corollary that the more an incumbent raises given fundraising parity, the worse the incumbent does!) Let me note again, when we do not control for D/R Fundraising Ratio, a challenger who raises a large amount of money will do far, far better than one who raises little money.
6. Running as an incumbent: + 2 points
The inherent incumbent advantage after accounting for money, party, district, and climate is not large. This doesn't mean running against an incumbent is just as easy as running for an open seat. However, the incumbency advantage may reside mainly in the ability to scare off opponents and scare off opponents' donors and supporters. If a challenger can manage to raise as much money as an incumbent, then the challenger has almost as good a shot as if the challenger were running for an open seat. However, 2 points is still an important amount.
7. Running against a first-termer: +1 point
First term incumbents are not much more inherently vulnerable than other incumbents, if at all. Even those who are in a seat that switched parties. This doesn't mean first-termers are safe, because they are more likely to attract high quality opponents with strong fundraising. When they do, however, they perform only slightly worse than a long-time incumbent under the same circumstances, on average.
8. Running against a self-funded candidate: +1 point
On average, running against a self-funded candidate might give a slight advantage. However, out of the 18 cases I found over the past three cycles, four showed the self-funded candidate underperforming by a massive 8-10 points. There may be a risk of completely blowing it by self-funding.
9. Running against a Republican incumbent in a Republican-gerrymandered district: +0 points
Looking at some states that were recently redistricted by Republicans in a partisan manner - FL, PA, MI, OH, VA, TX - there has been no benefit in performance for the Republicans. There may have been a slight benefit the first cycle after redistricting, followed by a slight underperformance later. The gerrymandering may have scared off opponents and their donors, however, which would certainly have been an overall benefit for the Republicans.
The following comparisons are specific to a just a few races, so we run into the problem of the statistics of small numbers, and can't really say what the average effect is. Also, in many of these races, the incumbent was tangled in more than one variety of misdeed.
10. Third party candidates: 0 to -15 points
In 2006 there were 16 House races where third party candidates garnered more than 4.5 percent of the vote. In 11 of these races the Republican underperformed by 4 or more points; in 6 races (2 in MN) the Democratic candidate underperformed by 4 or more points.
11. The Abramoff scandals: -1 to -12 points
Republicans in districts with links to the Abramoff scandal all underperformed: TX-22 (-1), FL-24 (-3), CA-4 (-4), AK-AL (-6), CA-11 (-7), and OH-18 (-12).
12. Alleged domestic abuse: -5 to -6 points
PA-10 (-6), NY-20 (-5): Not the good kind of press.
13. Threatenting your opponent: -5 points
WY-AL (-5), where Barbara Cubin told an opponent she'd slap him in the face if he weren't in a wheelchair. Cubin wasn't well liked anyway though.
14. The Delay scandal: +5 to -6 points
TX-22 (-1), AZ-1 (-2), NC-8 (-6), PA-6 (+5). Districts related to the Delay scandal don't seem to have been affected too much, although the Delay scandal certainly affected the national climate.
15. The Foley scandal: +1 to -3 points
IL-14 (-2), IL-19 (+1), FL-16 (0), NY-26 (-3). Again, no obvious severe penalty for those most closely related to the scandal or Foley's replacement on the ballot, but the scandal contributed to the national political climate.
Overall, these numbers seem to validate the strategy of supporting strong candidates in every district, against every incumbent. While it is certainly much more difficult for Democratic challengers to win against an incumbent in a conservative district, it is not impossible. It appears that with enough money, such races will often be competitive or near competitive in the current political climate. Another way to put it is that the competitive races in conservative districts in 2006 -WY-AL for example- were not simply flukes or outliers, but rather part of a larger pattern that is likely to be repeated in 2008.