To put this another way, Republicans/conservatives are not really more popular than they were in 2008 or 2006. But conservatives are increasingly synonymous with the GOP. That makes the GOP a more potent and manageable institutional force as well as making it virtually impossible for the nominal leaders of the party to ever settle for half a loaf or even 9/10ths of a loaf, which is essentially what President Obama is now offering. (Indeed, if you look at the negotiations last winter and these today you might even argue that they have difficulty settling even for the whole loaf. But that's another matter.)
People who follow politics closely know this. But Nate Silver has done the incredibly important work of actually putting together the numbers that demonstrate it.
When I castigate the Democrats for not having a clear message or President Obama for not having an "outside game" in the debt fight, readers will often write in to say that I'm ignoring the fact that the modern GOP is a coherent and highly ideological party while the Democrats simply are not. So Republicans are inherently more able to function as a unified force with a unified message than the Dems. In fact, these folks will argue, it's not even right to talk about "the Dems" because that buys into the illusion that they're a party like the GOP as opposed to a coalition of constituencies.
For my money, I don't find this a sufficient explanation. I do think the Dems are consistently guilty of what amounts to a political failure -- the failure to devise and push a consistent message and play on the weaknesses of their foes. I've made these points so often that there's no need (and probably appetite) for me to restate them here. However, it is important to note these structural realities that create a genuine tilt in the playing field of our politics, one that makes it easier for 35% to 40% of the electorate to dominate the country by having virtually total control over one of the two parties.
Still, structure isn't everything. Politics matters. And on that count the Dems continue to be captive and captured by a weakness it is in their collective power -- and for a president to a great degree individual power -- to change.