Nate Silver made the case this past Sunday in the NYT Magazine that Barack Obama will run a populist campaign because, all else equal, it works best for him in the electoral college.

Here’s the problem with that: Silver’s analysis depends on a massively unrealistic estimate about campaign effects. If the president goes populist, Silver speculates:

So let’s conduct a thought experiment. Suppose that against Romney, Obama does 10 points better among white voters whose households make less than $50,000 per year. The trade-off is that he does 10 points worse among whites making $100,000 or more and 15 points worse among whites making at least $200,000.

10 points! There’s no way that an incumbent president can move voters that much by any combination of 4th year rhetoric and promises.

Fortunately, we have a bit of evidence to look at. Silver says, and I agree, that the president has shifted to a more populist tone in recent months, with policies to match. Since Gallup keeps week-to-week crosstabs on its daily tracking poll, we can see what effect, if any, the shift has. The categories don’t match up perfectly — Gallup only gives us ethnicity and income (and education) variables separately. But if there’s any effect, it should show up, I’d say, in the income breakdowns. Gallup gives us four categories, by monthly income: the ones we’re interested in are below $2000 (or $24K a year) and above $7500 ($90K/year).

So: Obama gave his jobs talk to Congress on September 8. In the five weeks preceding his speech, the average approval rating difference between the “working class” and “rich” groups was 7 points (I’m using five weeks because the number jumps around quite a bit, as small-sample crosstabs in polls will do). And in the most recent five weeks, that gap has…been reduced, to under 6 points. Overall approval rating in the lowest income group went from 46.4% in August to 50.4% over the last five weeks; in the highest income category, the shift is from 38.4% to 44.8%.

Granted, these are not exactly Silver’s groups, but the fact that they moved together — and that there was more movement among the highest income group — is certainly suggestive. Of course, it’s unlikely that the president’s rhetoric had much to do with the shift, which (I think Silver agrees) was primarily caused by improving economic conditions, along with getting farther away from the ugly debt limit fight. But that’s the whole point; presidents really can’t do much by rhetoric and position-taking alone to affect approval, or, as we get closer to November, vote choice.

Now, none of this means that Silver’s advice to the Obama campaign is necessarily wrong. After all, even if the realistic maximum effects are closer to 1% than to 10%, well, Al Gore would have been very happy to get another 1% in Florida in 2000. Of course, whether the electoral college math works the same way at 1% or 2% instead of 10% is another question, as is the important question of whether the tradeoff Silver speculates about would really play out evenly overall, so that the campaign would merely be shifting where support comes from. So I’d still advise a bit of caution.

The larger point, however, is just to be very careful about anyone who claims very large campaign effects in general election presidential campaigns. The truth is that if they existed, we would know about it. Campaign effects in my view do exist…but we’re talking about very modest stuff, and my guess would be that’s even more minimized when we’re talking about an incumbent president, who is mostly going to be stuck with the reputation he’s built over the previous campaign and his time in office.

[Cross-posted at A plain blog about politics]

Jonathan Bernstein

Jonathan Bernstein is a political scientist who writes about American politics, especially the presidency, Congress, parties, and elections.