The Democrats don't turn out for midterm elections, and figuring out why can be quite confusing.

For example: you might hear someone say, "The demographics just don't work in Democrats' favor."

Why don't they?

- "For example: the Republican Party's constituency – older, whiter, male – comprise a higher percentage of the midterm vote than they do during general elections."

Well, those demographics did not matter as recently as 2006, when Democrats regained control of the House of Representatives and self-identified at 51 percent of the electorate. Similarly, even though the growing demographic groups have cast their lot with the Democrats (or vice versa), Republicans still manage to genuinely contest presidential elections.

- "Democrats do better when there's an aggressive presidential-style turnout machine to help candidates in marginal states."

Yes, but that same machine can be built for midterms and it doesn't seem to work as well.

- "Republicans aggressively gerrymandered districts, leading to a roughly five point asymmetry (in Nate Silver's phrase) in the average Congressional district, and this imbalance is locked in by intense polarization in Congress and because corporations can much more easily influence the electorate now."

That holds true for general election years, too. No intrinsic reason why it would be worse in off-year elections.

- "Democrats cluster more than Republicans."

True, with a hedge. The most Democratic congressional districts in the country are much more Democratic than the most Republican districts in the country are Republican, both percentage-wise and in real numbers. Democrats simply don't live in large enough numbers outside their bastions to regularly contest swing districts. And there are fewer swing districts, so the number of Democrats who would have an incentive to vote in midterms must also be shrinking.

Well, take a look at the past three midterm elections. They are unusual.

2002 defied trends. The president's popularity was either neutral or net-negative, and the economy was still shrinking. The post 9/11 hangover poisoned politics and scrambled the circadian rhythms of off-year campaigning. Republicans picked up 8 seats.

In 2006, 51 percent of the midterm electorate identified as Democratic compared to just 41 percent who identified as Republicans. Democrats picked up 30 seats and gained control of the House and the Senate.

In 2010, when President Obama acknowledged a midterm shellacking and Republicans picked up 63 seats, the percentage of the electorate identifying themselves as Democrats was 44 percent — same as the Republicans' 44 percent. But on the ballot itself, these voters chose Republicans 48 percent of the time, compared to 46 percent for Democrats.

Something other than turnout made the difference, even with a Republican tilt to congressional districts.

Look at voting demographics for both midterms, too. You'll see, as The Huffington Post did, that while the electorate is getting slightly younger and slightly less white, it didn't appreciably change from a year when Democrats won to a year when they lost badly. Harry Enten notes that the demographics of the 2012 and 2010 votes weren't dissimilar enough to explain the discrepancies between the performance of both parties in the two elections.

What this suggests is that "persuasion" — the ability to get voters to vote for a certain candidate — is alive and well as a tool for campaigns. Now, to some, persuasion is alchemy. To others, it correlates with variables that can be measured. For example, if the economy is better for you than it was, you will be more resistant to the message that the other party in power needs to be given a chance.

Or it means, as it did in 2006, that an unpopular president prosecuting an unpopular war will be punished by voters who have been motivated to vote on that issue.

Persuasion does not fully explain why the Republican Party can have such a horrible national brand and still manage to run candidates who win elections in legitimate swing districts.

In this cycle, there are reasons why Republicans will turn out in higher numbers than Democrats. There are reasons why those who do turn out, regardless of how they identify themselves, will vote for the Republican candidate.

Momentum is one. When the political class predicts and leans into a result, I believe it has a dampening effect on the motivation of the party that wouldn't benefit. That is, if everyone knows the GOP will win the Senate, why should Democrats bother, really? If, on the other hand, voters are bombarded with messages that races are really close, that the districts are competitive, and that no "wave" is expected, they'll be more excited about turning out. They are more powerful in those situations.

President Obama's approval rating is another. It is roughly a point higher than where George W. Bush's was in 2006. Voters do not yet sense the recovering economy, they see chaos in the world, and there is a lingering odor from (the ironically successful) ObamaCare roll-out.

In other words, if you hear pundits try to explain the election in terms of a midterm curse for Democrats, they're probably not worth listening to anymore.