At the end of this post I have some pretty pictures showing the near-uniformity of the vote swing from 2004 to 2008 (and thus, by implication, the importance of national rather than local or demographic factors in understanding what happened).
But before displaying these, let me discuss a particular factor that many have noticed: the differing voting patterns of people in different ethnic groups. Carl Bialik discusses an article by Steve Ansolabehere and Charles Stewart, who write:
Obama won because of race . . . Obama captured ten million more votes in 2008 than John Kerry did in 2004, resulting in a 4.6 percentage point swing toward the Democrats from 2004 to 2008. This swing did not occur similarly or uniformly among all politically relevant groups, as forecasting models might suggest. Most of the additional Democratic votes were cast by black and Hispanic voters--4.3 million and 2.7 million more, respectively. Democrats also gained among white voters, but the increase was a modest 3 million votes. . . . Obama gained not only by bringing new minority voters into the electorate, but also by converting minority voters who had previously been in the GOP stable.
This is consistent with instant election-night analysis (see item 4 here).
But I want to move on to a part of Ansolabehere and Stewart's article that I disagree with, and which I want to avoid becoming part of the accepted narrative of Obama's election.
They write, "had Blacks and Hispanics voted Democratic in 2008 at the rates they had in 2004 while whites cast 43 percent of their vote for Obama, McCain would have won." I don't think that's really a reasonable model, though, because that would be assuming that Obama would've outperformed Kerry more among whites than among nonwhites, which hardly seems plausible. To put it another way, Obama's baseline swing among any group is his national swing, not zero. Given the state of the economy in November 2008, zero just doesn't make sense as a baseline.
Similarly, Ansolabehere and Stewart write, "Had Obama relied only on a surge among young voters, holding other groups at the 2004 voting behaviors, he would have fallen short of victory." Again, I think this is slightly misleading: Obama's strategy was not to do better only young voters but rather to improve upon Kerry's performance in general, but piling up a particular margin among the young. Which is what he did.
You can also slice up the vote swing geographically, by counties in different regions of the country, and you find that Obama did close to uniformly better than Kerry nearly everwhere, except for Republican-leaning poor counties in the South (where Obama pretty much stayed even with Kerry). The geographic patterns are striking (see graph at the end of this post).
Race matters, yes, but we're still seeing a national swing.
Finally, I noticed that some of Bialik's commenters focused on Obama's racial appeal. I'd like to remind them that the Democrats gained even more in elections for the House of Representatives (compared to 2004) than Obama gained on Kerry. The House gains just weren't so obvious because they were spread over two elections.
2008 was a Democratic year, Obama was a Democrat, and he won in one of the ways the Democrats could've won. With a different candidate there might have been different demographics but roughly the same national swing, and maybe a slightly different electoral map with a similar electoral vote total.
I think Ansolabehere and Stewart are right on the money when they write, "the results of the 2008 election challenge much of what has been conventionally thought about race and politics in America. Barack Obama has accomplished an astonishing political move [by] disproportionately energizing nonwhite voters and converting erstwhile Republican supporters within the minority community without alienating white voters."
My summary: as Carl said, the election outcome is multidimensional. Because Ansolabehere and Stewart were writing a short article, they very properly focused on a single feature of the election--race. My disagreement with them over emphasis is in no way intended to represent a criticism of their scholarship. Once you want to break the vote down by demographics, I agree that ethnicity is the biggest factor (with age being an important predictor also, much more than in the past). But when it comes to the national outcome, I'd say that the #1 feature of the election was a bad economy that produced a national swing toward the Democrats in general and Obama and particular.
P.S. Comments here from John Sides. who links to this article by Mark Blumenthal and this by Marc Ambinder. John writes that "Most likely, the economy and race both mattered. Andy sees the economy as more important. I'm inclined to agree, but ultimately time, and more evidence, will tell."
My response: I'd say the economy was more important in determining the ultimate outcome of the election, and that race was more important in describing relative differences between the Obama and Kerry vote.
That is, the economy predicted the uniform partisan swing, and race described much of the discrepancies from uniform partisan swing.
P.P.S. Here's further discussion from Blumenthal.