Nate Silver does have a way with data visualization. His analysis of the Democrats' current electoral college edge includes a electoral scorecard that lists the 50 states in order of the margin of victory, beginning with Obama's wins and moving on to Romney's. The close states in the middle reveal a striking fact: Romney won only one state by a margin of less than eight points. Obama won eleven.
Forget for a moment the demographic contest -- one candidate's large advantage among whites vs. the other's larger advantage among all ethnic minorities. Forget, too, the strategic plusses and minuses of pursuing independents vs. turning out your base. Forget national popular vote margins. The simple fact is that Romney won only one state that any Republican would not have won. A dozen states were competitive, and Obama won eleven of them -- by margins that were increasing rapidly at the end, and exceeded the final polls. He outperformed on every front --turnout, targeted advertising, and ultimately, the debates. He just kicked Romney's ass across the political field.
Update: it occurs to me that Silver comes to a very different conclusion: that even if Romney had won the national popular vote by two percentage points, Obama still would have won the electoral college. That is, Obama's advantage was structural, and would be shared by any Democrat at present. That assumes, I believe, a proportionality between Obama's margins in the swing states and the popular vote totals. But most of the direct competing was done in the swing states. The tipping point, in Silver's reckoning, was Colorado: that is, Romney would have had to win Colorado and every other state that Obama won by a lesser margin than Colorado (Virginia, Ohio, Florida) to win the election. And Obama won Colorado by 4.7 percentage points -- quite a large margin for Romney to have overcome. Does that mean that Obama's advantage was structural, i.e., that no competent Republican could have overcome it this year? I don't know. The margin there, and in all the truly competitive swing states, seemed much smaller just a few days before the election.