Over at RealClearPolitics, you can find a valuable exchange between RCP’s Jay Cost and TDS Co-Editor Ruy Teixeira over the latter’s “New Progressive Majority” study published recently by the Center for American Progress.
A few days ago, Cost questioned Texeira’s confidence that the demographic trends he documented in the study represented a reliable indicator of future presidential election cycles, suggesting that short-term factors including campaign dynamics are often crucial variables. Texeira’s response notes that he’s dealing in trends and probabilities, not predictions or certainties, and makes this point about perennial “short-term factors” dismissals of electoral results:

Of course, there are some–Cost appears to be one–who argue that all elections are not much more than short-term forces and that’s all you need to look at. By that logic, the election of Ronald Reagan in 1980 was all about short-term discontent with Carter and the economy and the shifting patterns of support compared to twenty years previously were not of much significance. But that wasn’t true then and I suspect the argument that Obama’s victory was all short-term forces will also turn out to be incorrect.

In a wrap-up post, Cost partially concedes some of Teixeira’s arguments, but notes the strong belief of Republicans as recently as four years ago that trends were moving permanently in their direction.
The whole exchange is worth reading. But while Jay Cost raised some good questions about the implications that some Democrats might draw from Teixeira’s study, he didn’t lay a glove on Ruy when it came to the data.