"State Fundamentals" And the 2012 Senate Contest

According to the forecast from FiveThirtyEight, Nate Silver's famous election forecasting site, Democrats are currently expected to hold 52.4 Senate seats after this election on average, a decline of just 0.6 Senators from their current position, and are given 86.4% odds of retaining the chamber. Those are some nice numbers for a year when Democrats were expected to get pretty well hammered. They've got Democrats leading solidly in MA, RI, NY, NJ, PA, DE, MD, OH, WV, MI, MN, CA, and WA, with rather robust leads in HI, NM, MO, WI, VA, CT, and FL, plus a tiny lead in IN. Republicans have modest leads in MT, ND, NV, and AZ, with a stronger lead in NE and locked-down leads in TX, UT, WY, TN, and MS. Independent candidates are projected to win in Vermont and Maine, both rather solidly. If you were to just "call" each state according to who's favored to win it, however slightly, you'd get 53 Democrats, including Bernie Sanders and Angus King, maintaining the status quo in overall caucus membership.

But digging into the numbers a bit, we find that there are a lot of important states where FiveThirtyEight is assuming that partisan gravity will play a really substantial role. In Arizona, for instance, the "adjusted polling average" has Republican Jeff Flake leading Democrat Richard Carmona by just 0.4%, but the "state fundamentals" say it's an R+8.3% state, so overall they've got Flake winning by 1.9%, and sporting a 62% chance of victory. In Connecticut, Democrat Chris Murphy's lead over Republican Linda McMahon is just 1.7% in the adjusted polling, but the +19.1% Democratic fundamentals number turns the whole race into Murphy +4.4%, 74% chance of victory. Indiana adjusted polling gives Democrat Joe Donnelly a 2.7% lead, but the fundamentals say it's Republican Richard Mourdock by 1%, so Donnelly's lead is just 0.3% in the forecast, and just a 52% chance of winning. In Montana, Democratic Senator Jon Tester holds an 0.6% lead in the adjusted polling, but Republican Denny Rehberg is favored by the state fundamentals by 8%, giving him a 1.6% lead overall, and Tester just a 38% chance of holding his seat. In North Dakota, adjusted polling shows a tied race between Republican Rick Berg and Democrat Heidi Heitkamp, but Berg takes a 4.9% lead in the forecast on the strength of a 10.5% lead in the fundamentals, and Berg is given 78% odds of victory.

That's a lot of key Senate contests being very heavily affected by our a priori assumptions of the race. That's not to say that FiveThirtyEight is doing anything wrong by adjusting for state fundamentals, and we can see that states with more robust polling are giving less weight to the fundamentals. But it is interesting to observe. As I read the landscape, the battle for control of the Senate is being fought on Democratic terrain in the East and Midwest, in Wisconsin, Missouri, Ohio, Florida, Virginia, Connecticut, and Massachusetts. But the battleground in which Democrats will seek to expand their majority is Western Republican terrain: Montana, North Dakota, Nevada, Arizona (okay, and let's give Indiana a special exemption, even though it's not western). If you're a believer in partisan gravity, then you would expect Democrats to squeak through the one blue-state defensive contest where the polling's been a bit scary, namely Connecticut, and to pull through the toss-up races, but not to pick up the Republican-held seats out west. If partisan gravity fails to show up, though, Connecticut will be very close, although probably will still go for the Democrat, but Montana, North Dakota, and Arizona become very interesting. Tack on those three states, plus a slightly more solid lead in Indiana, and Democrats could get to 56 seats without even winning in one of the more Hispanic states in the nation, Nevada.

In one way it will be an interesting test of modelling assumptions. In another, it's a demonstration of the need for more polling. These Senate contests in small states with non-competitive Presidential contests are important. People need to be polling them. That they are not doing so is not okay.