I'm looking at some data about the outcome of the 2016 election, and even though I think I'm quite politically tuned in, I must be missing something.

My question is pertaining to California's 21st US congressional district. According to data provided by the California Secretary of State, this is the breakdown of voter registration by party for their roughly 225,000 people that registered to vote:

  • 46.37% were registered Democrats.
  • 29.00% were registered Republicans
  • 2.41% were registered independents.

And yet, the Republican in that district won by a margin of 13.4 points. In fact, as of October 24th 2016, there were apparently only 65,323 registered Republicans, but the Republican candidate garnered 75,126 votes versus the Democrat's 57,282 votes.

Can someone please explain this to me? I mean, I get that some registered Democrats may have voted Republican, but by these margins?

I'm not normally one to don a tinfoil hat, but what the hell is going on?

  • This isn't necessarily an explanation, but incumbents generally have a very strong advantage over challengers regardless of party affiliation unless they've really botched things in such a way that a challenger can run effective attack ads. Combine that with the fact that this candidate is a relatively moderate republican and he endorsed Jeb it isn't too surprising to see some dems vote across the isle, but I agree that those are some oddly large margins
    – Gramatik
    Nov 29, 2017 at 17:18
  • Not worthy of an answer as it's speculation, but the Trump vs Clinton campaign ended up polarizing the Republican voters heavily ensuring a strong turnout. On the other side, Hillary and a few scandals caused trust issues and disillusionment that caused Democratic voters not to vote. This is somewhat based on the argument that Bernie Sanders would have done a better job for the Democrats as he would have done a far better job of mobilizing/polarizing the Democratic vote (not necessarily a better job of attracting new votes)
    – Twelfth
    Nov 30, 2017 at 19:57

2 Answers 2


You're getting confused in part because you're looking at the wrong number for independent voters. California lets you register as an independent, but it also lets you register as an American Independent and member of the American Independent Party (a far-right party that is famous for endorsing George Wallace's presidential campaign). People who aren't a member of any party are instead supposed to register as "no party preference," which you can find on the next page of the registration data. 20.72% of voters in the district registered this way. It's also likely that at least some American Independent voters wanted to register as no party preference and got confused; a poll of AIP voters found that 73% thought they were registering as independent from all parties.

With that, the full 21st district registration numbers are:

  • 104,464 (46.37%) Democratic Party
  • 65,323 (29.00%) Republican Party
  • 46,673 (20.72%) No Party Preference
  • 5,437 (2.41%) American Independent Party
  • 1,202 (0.53%) Libertarian Party
  • 880 (0.39%) Peace and Freedom Party
  • 452 (0.20%) Green Party
  • 849 (0.38%) Other

This totals to 225,280, which is the number of voters registered in that district. And with these numbers, it looks a lot more reasonable for a Republican to win if they capture a lot of independent voters and have better turnout.

  • 7
    There's also the fact that many Republicans register as "Democrats" in Democrat-dominated areas (like California, for example) which have closed party primaries; on the account that they don't need to bother voting in R primary due to R's rarely winning congressional seats and D primary being where the actual congresscritters are decided - voting in which requires one to register as a Democrat in case of a closed primary.
    – user4012
    Nov 29, 2017 at 18:41
  • CA has "modified closed" primary that works differently though; not sure if the same effect happens there
    – user4012
    Nov 29, 2017 at 18:47
  • 3
    @user4012 - and, you know, maybe the GOP candidate was just plainly better. Nov 29, 2017 at 19:37
  • 1
    @PoloHoleSet - less likely. People don't often cross party lines these days, as far as I recall 538's stats
    – user4012
    Nov 29, 2017 at 19:40
  • @user4012 My Probability & Statistics professor said that was the logical way to decide how to register to vote. That way you get to influence the nominee most likely to win the general election. Nov 29, 2017 at 22:17

The winner, critically, is the incumbent and one of the more moderate Republicans. Moderate incumbents often hold on to districts that would probably vote for the other party given a clean state, in both directions.

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