Very interesting analysis by Nate Cohn in last week's New York Times that showed why Democrats are unlikely to win a majority in the House of Representatives while winning statewide majorities for Democrats. Democratic voters are clustered in cities giving huge margins of victory to Democrats while leaving many more slim Republican majorities in more rural districts. Look at the voting pattern of a few states to see the situation:
So while Pennsylvania and Ohio will vote Democratic as a state, handing their electoral votes to the Presidential candidate and putting Democrats in the Senate, they will send more Republicans to the House than Democrats. Same goes for many other states, enough to hand the House to Republicans for many years to come.