Palin's effect on the 2008 election

The usual political science wisdom on vice presidential candidates is that they have very little effect on presidential election results. The most they usually do is improve their parties' prospects in their home states, and when their home states are places like, say, Alaska and Delaware (states that are tiny and reliably in one party's corner), that doesn't make much of a difference to the Electoral College.

But there's a lot of talk going around that Palin was the exception. Due to her outsized personality or a ton of media coverage or whatever, the story goes, she may have had a big impact on the vote. Maybe she rallied a somewhat depressed conservative base to get out to the polls. Maybe she cost McCain the support of prominent endorsers like Colin Powell. Maybe these effects cancelled each other out.

Back in April, John Sides wrote up a paper by Richard Johnston and Emily Thorson allegedly showing a huge Palin effect. Matt Yglesias cited this study last week. The paper produced three very interesting graphs showing that voters knew the economy was tanking long before they started turning against McCain, and also showing a very close relationship between voter approval of Palin and of McCain. The interpretation is that Palin, not the economy, cost McCain the election:

Judgment on her was incontestably important. The correspondence between dynamics in her ratings and dynamics in McCain vote intentions is astonishingly exact. Her marginal impact in vote-intention estimation models dwarfs that for any Vice-Presidential we are aware of, certainly for her predecessors in 2000 and 2004. And the range traversed by her favorability ratings is truly impressive. But why? We are unaware of any theory that opens the door to serious impact from the bottom half of the ticket.

I'm going to somewhat disagree with this interpretation of the graphs. For one thing, it shouldn't be a shock that a presidential candidate's approval rating moves in tandem with that of his vice presidential candidate. If you're going to vote for one, you're going to vote for the other -- people know that. (Indeed, it's more surprising that Obama's and Biden's ratings don't jibe more.)

Second, while we would expect the incumbent party's candidate (in this case, McCain) to bear the blame for a sour economy, we wouldn't necessarily expect voters to make that connection overnight. It was a confusing and very sudden collapse in the financial sector that caught the public's attention in mid-September. It probably took a few weeks of campaign noise and media coverage for voters to apply the information to the political sphere.

Finally, note where the McCain plunge begins -- right around October 8th (pace Dave Barry). What happened that week? Well, October 7th was the night of the second presidential debate, the town-hall format one that included McCain's famous "that one" reference to Obama. That debate turned mostly on economic matters, with the candidates charting out different positions on how to rescue the economy. Sixty-three million people watched the debate - a 21% increase over the first Obama-McCain debate and the biggest viewership for a presidential debate since 1992.

So here's my interpretation: By the 2nd week of October, voters recognized the economy was tanking. The high public attention on the 2nd debate gave voters an opportunity to apply their knowledge of the economy to the political world, and they chose to blame the economy's collapse on the incumbent party. Palin was along for the ride on this. Her star was tied to John McCain's, and his to the interaction of party and economics.