In retrospect, the problem for Democrats was that some in the party—particularly in the liberal wing that is dominant in the House of Representatives—seemed to read this shift away from Republicans as a shift to the left. That became apparent first in the early-2009 construct of an economic stimulus package, written initially in the House. It went heavy on the kinds of public-spending programs liberals favor, and light on the tax cuts and small-business incentives that even more moderate Democrats like…

Yet the absence of an ideological shift can be seen by looking inside Wall Street Journal/NBC News polling throughout the last four years, the period when political winds were shifting so dramatically. The one constant has been voters’ ideological balance, which is virtually unchanged…

The reality is that Democrats were renting a lot of centrist voters in 2006 and 2008, but didn’t really own them. And now Democrats seem to be losing their grip on some of those centrist, independent-minded voters.