John Harwood NYT:

From one vantage point, recent advances on race, gay rights and health care give the impression of powerful momentum for America’s liberal Democrats.

But inside one of Washington’s power centers, they are running straight into a wall — and are unlikely to break through it for a long time. Among the ironies of the rapid shift on cultural issues is the inability of Democrats to profit from it in the House of Representatives.

Republicans hold their largest House majority since the Great Depression, holding 246 of the 435 seats in the House, meaning that Democrats must pick up 30 spots to regain a majority. The power of incumbency and the effects of polarization, which has dramatically shrunk the number of voters up for grabs, make gains of that magnitude excruciatingly difficult.