Do endorsements matter?

I’m not asking that question rhetorically, or with an excess of snark. I’m honestly interested to know. Have you, loyal readers, ever decided who to vote for based on their endorsers? Do you know anyone who has?

We’ll have a chance to see the real-life impact of Edwards’s endorsement of Obama next week in the Kentucky primary, a state similar to West Virginia in that it’s comprised largely of white folks with blue collars. Hillary has led in that state consistently since polling started: according to RCP, her lowest total of victory in the polling was 25%. The average right now sits at a 28.7% spread, and SurveyUSA has predicted a margin of victory as high as 34 points.

I think it’s fair to say, then, that Clinton is favored by anywhere from 25-34 points. The question is this: will Obama beat that spread? And, if he does, will it be the effect of the Edwards endorsement? Let’s say Obama manages to lose by ‘only’ 15 points (a pretty rare feat for a presumptive nominee, but I digress): Does he owe the extra ten points to Edwards?

I tend to think not, that there are other factors in play (increasing recognition among Dems that Obama is the nominee and rallying behind him would be the main one). Furthermore, I think that endorsements, like justifying a VP pick based on electoral college math, are entirely pointless. I’d say it’s fair to point to the example of Edwards himself as proof of that: not only did John Kerry lose Edwards’s home state, North Carolina, by five more points than Al Gore did, a cursory glance through my Almanac of American Politics suggests he lost the entire region of the South more vigorously than his predecessor.

But I don’t know. Is anyone aware of any statistical proof that the endorsements by other politicians matter? Note: Some endorsements do matter. Union endorsements matter, for example. But that’s because unions already control a large bloc of voters who rely on their leadership to tell them what to do. Having transcended the age of the political machine, politicians control no such loyalty and can deliver far fewer votes.