What the N.C. Republican primary means for Senate polarization

 


Thom Tillis, right, and his wife Susan Tillis greet supporters at a election night rally in Charlotte, N.C., after winning the Republican nomination for the U.S. Senate Tuesday, May 6, 2014. (AP Photo/Chuck Burton)

The victory of N.C. House Speaker Thom Tillis in Tuesday’s Republican Senate primary has major implications for whether Republicans can knock off Sen. Kay Hagan in November. But there’s one other important implication of his victory: by defeating his conservative challengers, particularly tea party favorites Greg Brannon and Mark Harris, Tillis may have prevented at least a bit of further polarization in the increasingly polarized Senate.  Here’s why.

Below is a graph that plots estimates of the ideology of the three frontrunning Republican candidates: Tillis, Brannon, and Harris.  For the sake of comparison, I’ve included Hagan, the more liberal Elizabeth Warren, and two Senate Republicans: Chuck Grassley and Ted Cruz.  The measures of ideology come from Stanford political scientist Adam Bonica.  Bonica relies on campaign donation data to estimate ideology.  The logic is this: by looking at patterns of which donors give to which candidates, you can discern how liberal or conservative those candidates are.  If, for example, a first-time candidate raises money from donors that tend to give to well-known conservative incumbents, then this new candidate is likely to be a conservative, too.


What Bonica’s data show for these four sitting senators is pretty intuitive.  Warren is to the left and Hagan less so.  Cruz is to the right and Grassley less so.

But what they show for the North Carolina GOP candidates is more interesting. Were Tillis to win in November, the Senate would be getting someone whose political beliefs look much more similar to Grassley’s than Cruz’s.  By contrast, Brannon’s views are closer to Cruz’s and Harris is estimated to be even more conservative than Cruz.

Of course, we don’t know whether Tillis will beat Hagan.  Our forecast sees Hagan as the current favorite but other forecasts see the race as a toss-up.  Nevertheless, nominating a relative moderate likes Tillis probably helps the GOP win, since political science research shows that strongly ideological candidates can be punished at the ballot box. What this analysis shows is that a Republican victory in November will contribute a lot less to Senate polarization with Tillis as the nominee instead of Brannon or Harris.

John Sides is an Associate Professor of Political Science at George Washington University. He specializes in public opinion, voting, and American elections.

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John Sides · May 6, 2014