At RealClearPolitics today Sean Trende and David Byler unveil a gizmo that enables you to assess the overall electoral impact of changes in the turnout rate and partisan preferences of various demographic groups, with 2012 serving as a baseline. It’s great fun, and instructive, too. While most of it is mechanical, there is one very important assumption the authors note: it assumes a “uniform swing” of demographic groups in various states, which actually almost never happens. This is not a merely technical matter: “uniform swing” rejects the impact of targeted appeals by campaigns to battleground states, and also happens to make what happens with Latino voters significantly less relevant since so many of them are “wasted” by living in non-competitive states like California and Texas.

In any event, aside from the gizmo, Trende and Byler go on to articulate the central dilemma in projecting what might happen in 2016 from recent trends in turnout and vote share: how much of the patterns seen in 2008 and 2012 are attributable strictly to Barack Obama? And does the fact that Republicans did vastly better in 2010 and 2014 than in 2008 and 2012 a function of oscillation between presidential and midterm cycles (as I argued in my own book on 2014), or instead a “reversion to the mean” in turnout and preference patterns due to Obama’s absence from the ballot? These alternatives have diametrically opposed implications for the 2016 baseline.

[N]ote the impact of a potential reversion to mean in vote share and turnout among African-American voters. While Republicans won only 4 percent of the black vote in 2008 and 6 percent in 2012, the typical Republican vote share is between 9 and 11 percent. Note also that, historically, African-American participation has lagged white participation by about six percentage points: Black participation lagged white participation by five points in 2000 and 2010, by six points in 1998, 2002, and 2014, and seven points in 2004. The gap was 11 points in 2006.

So the question is: Is the mid-single-digit vote share Republicans received in 2008 and 2012 the rule now? Likewise, is African-American participation going to be equal (or slightly ahead of) white participation going forward? Perhaps the best argument for a reversion to mean is that African-American voting patterns and participation rates in 2010 and 2014 looked an awful lot like those of 1998, 2000, 2002, and 2004. This suggests that President Obama’s popularity among African-Americans may not be transferrable.

On the other hand, perhaps, as some have suggested, there is a newly emerging, fundamental difference in voting patterns between the midterm electorate and the presidential electorate. We certainly don’t dismiss this possibility. After all, voting is habit forming, and after marginal voters have cast ballots in two presidential elections, are they really marginal voters anymore?

As we get closer to the 2016 general election, it should be possible with careful scrutiny of polling data to get a sense about which proposition is likely to be more accurate. But I must say Republicans seem more convinced by “their” construction of the facts–that 2014 shows the wave of the non-Obama future–than are Democrats by “theirs”–that they have a built-in advantage in presidential years. That’s worth keeping in mind when weighing the importance of electability in either party’s presidential nominating process.

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Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.