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How much of the change from 2016 was due to different people voting vs. the same people changing their vote choice?

A colleague writes:

Whenever I think of appropriate democratic strategies for 2020 I am drawn to ask how a candidate can get voters from Trump.

But a colleague frequently corrects my thinking by saying Karl Rove discovered that you want to rile up your base to get them to turn out and appealing to the median voter is nonsense. He is not the only one who says so.

Is there any evidence you have seen on the Rove hypothesis? What is the best evidence I wonder? Strikes me as a hard thing to study but terribly important.

I guess the first question I would have is how many people vote sometimes (say 30-80% of the time) vs. how many vote sometimes democratic (30-80%) of time. What is the size of the two pools? Harder to get at of course is the elasticity or ease of changing those numbers. But if you assumed they were equally easy to shift, then the size of the pools would be determinative.

Or if the size was comparable and your prior was that shifting a political opinion is very hard but getting someone to decide to vote on a given occasion vs. stay home (if they sometimes vote) is less hard, then maybe with equally sized pools, you know the answer.

Before giving my answer (or, more precisely, Yair’s answer), I’ll just point out that the same question could be asked from the Republican side. Given that the Democrats are doing various things to try to win more votes in 2020, the Republicans can hardly just stand still in this new election and expect to squeak by again. So, although my colleague poses the question from a particular partisan perspective, it applies from either direction.

OK, now to the answer. It turns out I already posted on the topic in May, reporting a detailed analysis from Yair Ghitza, who asked:

How much of the change from 2016 was due to different people voting vs. the same people changing their vote choice?

and who concluded:

Two things happened between 2016 and 2018. First, there was a massive turnout boost that favored Democrats, at least compared to past midterms. . . . But if turnout was the only factor, then Democrats would not have seen nearly the gains that they ended up seeing. Changing vote choice accounted for a +4.5% margin change, out of the +5.0% margin change that was seen overall — a big piece of Democratic victory was due to 2016 Trump voters turning around and voting for Democrats in 2018.

And lots of data-rich detail in between.

I’m reposting because it seems that at least one potential reader didn’t see this when it came up the first time.


  1. jim says:

    There was an interesting piece on 538 a while back (unfortunately I can’t find it now). It bemoaned the fate of democrats, insinuating the law favors republicans because of the electoral college, the equal by-state representation in the senate, and the non-statehood of DC and Puerto Rico.

    This hilarious piece, like your correspondent above, seems to have forgotten that there is a fool-proof way for either party to get more votes and win more representation: change it’s friggin’ policies and move to the &*^#)#&^ center!

    That’s what Clinton did. That’s what Bush II did. That’s what Obama did. Even Trump did it, espousing an end to fighting in Afghanistan and talking up the rebirth of American manufacturing, and talking down free trade – hardly standard Republican fare.

    There just aren’t enough hardcore party loyalists to win elections. Elections are won, and always have been won, in the center, by people changing their votes to vote for the candidate that’s the least objectionable.

    • Martha (Smith) says:

      Brings to mind the time my Mom voted Democratic for President, and Republican for Governor — and my Dad did just the opposite.

    • Andrew says:


      There is some evidence of electoral benefit to political moderation—see here, for example—but the structure of the system does matter. For example, Hillary Clinton moved to the political center on many issues and won the popular vote by 2 percentage points. My guess is that had the less centrist Bernie Sanders been the Democratic candidate, he would’ve done worse in the vote—but he may well have won the electoral college. In the 2018 Congressional races, neither party moved toward the center and there was a big shift to the Democrats, explainable in part by voters wanting party balancing (which represents an aggregate preference for more centrist policies).

      My point is that, yes, on average voters prefer the center, but there are different ways for this to happen. It can happen through shifts in party positions on various issues, it can happen through choice of candidates, it can happen through turnout, it can happen through persuasion or through voters deciding on their own to switch, it can happen through party balancing (as in Martha’s example in this thread), etc.

      • MP says:

        Can you expand on this “party balancing” idea? I have trouble seeing any voter thinking “Those other guys are electing a bunch of lunatics. I’d better vote for our lunatics to balance it out!” On the other hand, that does seem like what is actually happening.

        • Andrew says:


          See this post, What is “party balancing” and how does it explain midterm elections?

          Also, they’re not lunatics, they’re just politicians. There are two natural reasons to favor party balancing. The first is for checks and balances, as one-party government can lead to corruption and extremism. The second is for policies, if you feel that your preferences on some key issues are between the policy options offered by the two parties.

          Finally, I don’t think that most voters do party balancing. Most voters are pretty consistent partisans. But some voters do party balancing, and that can make a difference.

          • Anoneuoid says:

            Id say the US already has a one party system. No matter which party is more powerful there is more spending, more debt, more overseas military operations, more spying on the populace, more free money “loaned” to super wealthy giant banks, more merging of corporate and government power, etc.

            Different excuses for doing this are used by those calling themselves Republican vs Democrat, but same end result.

          • MP says:

            Thanks Andrew. That does make sense. I had a picture of people reacting to extremism (real or perceived) from the other party by supporting politicians on their own side more extreme than their own views, in an effort to balance things overall. But splitting a ticket to try to achieve overall balance, I can certainly see that happening, at least for some voters.

            And fair point re “lunatics”. That was flippant.

          • jim says:


            After reading a good share of your paper, I concede that it’s not so easy to blithely say that moving to the center results in more votes. It’s pretty complicated.

            But I wasn’t quite clear on the 2% idea in your paper: is that based on all elections that you studied? Because, like in many things, there are a extreme cases that can be easily excluded from the overall sample of elections which, it would seem, might raise the stakes. I know your paper discussed that but I wasn’t clear on exactly what the 2% represented.

            Also, I wonder: how much stock do you put in your conclusion? After all, as you say, it’s “causal inference” – not “causal demonstration” so there are many sources of error. So what do you think?

      • jim says:

        I agree with your point that the center can be won in a variety of ways – including balancing.

        But using tenuous conclusions – and I think any conclusions about what voters are thinking are necessarily tenuous, we really have to keep that in mind – extracted from analysis of the most recent election to make general claims about the impacts of centrist policy on elections in general won’t yield accurate results.

  2. Shecky R says:

    Another confounding problem is that in the end most voters probably vote viscerally — they simply do or don’t like a politician’s personality, speaking style, voice, appearance, etc. As much as voters SAY they want to hear specific policy positions, when candidates actually offer wonky details voters yawn and turn off. And for many voters there are only 1 or 2 issues that actually matter and can sway their vote anyway.

  3. Anoneuoid says:

    Under democrats we get legalized propagandizing to the American populace:

    Under republicans we get legalized falsifying of the budget:

    I could go back further with obviously the patriot act, etc. But the point is that government corruption just continues to increase no matter which of these parties is in charge.

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