We found that at least one endorsement really can make a difference: that of a state party.
In a forthcoming paper with Political Research Quarterly (ungated version here), Thad Kousser, Eric McGhee, Scott Lucas, and I look at party endorsements in two different ways, arriving at very similar results. Our first approach was to conduct a survey experiment on 1,000 Californians during the primary in June of 2012. (California has a “top-two” election system, in which candidates of many parties compete against each other in the June primary.) We briefly described to the respondents three fictitious candidates: a “traditional” Democrat, a “business” Democrat, and a Republican. We then randomized an endorsement by the Democratic Party between the two Democrats, and asked voters whom they preferred. The endorsement made a big difference, particularly for the traditional Democrat, whose vote share increased by around nine points when respondents heard that the party backed him.
Our second approach was to examine the actual results of the June 2012 election, looking to see whether endorsed candidates outperformed others. This is tricky to measure, since if you just compare the vote shares received by endorsed candidates with those received by unendorsed ones, you find huge effects: Endorsed candidates seem to do 40 or 50 points better. But that’s because candidates who get endorsements tend to be better candidates to begin with — they’re better fundraisers, better public speakers, are better fits for their districts, etc. The key is to figure out what the endorsement does for these candidates on top of all their other advantages.
To really measure the effect of the endorsement, we had to compare candidates of very similar quality. We did that by collecting the internal party endorsement votes conducted within local Democratic party committees. This way, we could see if candidates who had a lot of support within the party but fell just short of the endorsement threshold did notably worse than those who just passed the threshold. (This research approach is known as regression discontinuity.)
Some results can be seen in the figure below. The internal party endorsement votes are depicted along the horizontal axis (with zero the point at which the endorsement occurs), and the primary vote share lies along the vertical axis.
What the graph shows is that the party endorsement mattered. Candidates who just barely eked out endorsements are presumably no better or worse politicians than those who fell just short of it, but the former got a substantially larger chunk of the primary vote than the latter. Depending on how we ran the analysis, we found an endorsement effect of somewhere between seven and 15 points.
This isn’t necessarily an enormous effect. A particularly skilled or lucky candidate could beat the party’s preferred one, but not easily. What this study does show is that those who receive this one endorsement get a substantial advantage in the primary election, and this is an endorsement worth fighting for.
This study also shows that parties are more than just cheerleaders for particular candidates; they can make them or break them. The reason party insiders are usually happy with the sorts of nominees they get is because they play a large role in picking them.
Thad Kousser is a professor of political science at the University of California at San Diego. Scott Lucas is the Politics editor for the Las Vegas Sun.