What you need to remember about the House is that it’s not representative of “the public,” it is representative of 435 different publics. If you want to understand the difference, consider this.
Assume you have 100 voters, 55 of whom vote Blue and 45 of whom vote Red. In a straight up election, the Blues will win every time. But if you separate them right, you can actually cause the Reds to win overwhelmingly. Indeed, the Reds could win as many as 8 of 10 districts if you can divide them right. Thus, even as the Blues win the national election by 10%, they could lose as many as 80% of the districts.
This is what is happening in the House.
The House is divided into 435 districts. Because of Republican wins in 2010 at the state level, the Republicans controlled the redistricting process for 213 of the 435 seats. The Democrats controlled only 44 seats. The rest were split.
As a result of this, 109 Republican seats were made more safe for the Republicans and another 109 Democratic seats were made more vulnerable to the Republicans by adding Republican voters or removing Democratic voters from those districts. That gave the Republicans a competitive boost in 218 districts -– they only need 218 to control the House -- by skewing the chances in those districts toward the Republicans. The Democrats, meanwhile, managed to make only 67 Democrats seats safer. This means the Republicans will win more seats even if they lose the popular vote. And indeed, in 2012, the Republicans won 33 more seats even though they lost the popular vote to the Democrats by about 0.5%.
Moreover, this is making these seats safer, which means few seats remain competitive. Since the 1990s, the number of competitive seats has fallen to around 40 -- less than 10% of all seats. This is why 99% of incumbents got re-elected in 2002 and 2004 and why 90% got re-elected in 2010.
So don’t believe that the Republicans winning the House means anything about the party’s health on a national level. In fact, the Democrats weren't concentrated in a small number of state... remember every vote at 50%+1 is a waste... the national elections and the Senate would look even uglier. Do not listen to anyone who tells you that the party is fine or who points to the House as evidence of that. The party is not doing fine and it needs to realize that real change is needed.
Finally, I want to highlight a point that was made in the comments the other day which I think should give everyone pause: the Democrats can run competitively for Senate seats in every state. . . the Republicans can't. That should tell us something. We need to broaden our appeal and again become a national party, not a party of 218 House Districts.