Democrats have won the aggregate vote for House seats according to the statistics tabulated so far by 53,952,240 to 53,402,643--over half a million votes as Ian Millhiser points out. Of course Democrats didn't actually win the House because of severe gerrymandering by Republican state legislatures after the debacle of 2010.
I fear that President Obama's victory has not put future 2010s behind us unless the cleverness and good organization of his presidential campaign are turned to downballot elections, including at the state legislative level. We cannot move the government to the left without local organizing and without working to turn red states blue.
We should commend Messrs. Messina, Plouffe, and Axelrod for their insight that canvassing and personal contact with voters is the best way to encourage voters and to counter Republican money. But sustained local precinct organizations, which make sure voters are contacted by their neighbors, repeatedly, over years, are the strongest way to build a Democratic majority. Early canvassing focusing on persuading the persuadable could help translate a progressive program into a progressive victory.
These longterm organizations don't exist in most places the way they do in some areas of New York City. I don't know precisely how we build that on a national scale, and the centrist centralizers in Washington tend to distrust organizations they don't control especially if they push the party left. Hence the negative reaction of elitists like Rahm Emmanuel to Governor Dean's famous fifty state strategy. But to prevent another 2010 we need national subsidies, in the form of both money and training for local grassroots organizers building a permanent local Democracy of neighbors, including in states that are now Red.