Why is the GOP so good at ultra narrow wins?

[Virginiá]

It seems that the GOP is simply better at turning out their voters than the Dems are.  In a tossup race, it's usually the side with the better turnout operation that wins it.  Other than Obama's two wins, Dems have probably not won the turnout war since 1992 or earlier.

I don't think it is so much about being better at turning them out than it is about Republicans counting some of the highest turnout demographics as part of their base. Old people, the wealthy and well educated are all naturally high turnout voters and also currently Republican-leaning. Meanwhile, Democrats rack up huge margins among minorities and young voters, both of whom generally have some of the lowest turnout rates.

[Virginiá]

I was thinking more of white college educated voters, who despite trending some towards Democrats this generation are still more friendly downballot with Republicans and usually still end up voting for the Republican presidential candidate, even if just barely. Though, polling-wise, generic ballot polls do have Democrats leading with them pretty often. Postgraduate voters are a comfortable Democratic group, though.

Further, while I don't have the data right now, I'm willing to bet the support among white college graduates for Democrats is even more nuanced. Younger grads are probably more Democratic than older ones (If it's anything like the overall age divide, the gulf is probably big), which gives Republicans an advantage even if they might be numerically weaker, although this is already factored in when you look at the overall results for that demographic.