A reader writes:
I want to dispute the suggestion from your reader that African-Americans only voted for Obama because of his race. African-Americans voted for him in nearly the SAME proportion as for Kerry in 2004 and Gore in 2000. In 2000, Gore got 90% of the black vote. In 2004, Kerry got 88%. In 2008, Obama got 95%. Obama got a relatively "slight" bump. So let's dispatch with this nonsense that blacks overwhelmingly vote on the basis of skin color. They have shown for decades that they are quite happy to vote for a white candidate, specifically the candidate they perceive has their interests in mind (or at least not openly hostile to their interests).
But what about Democratic primaries? In 2008, Obama enjoyed a 9-1 advantage over Clinton among African-Americans. And the only other time a black candidate and white candidate were neck-in-neck for the nomination?
The Rev. Jesse Jackson garnered three times as many white votes in the 1988 primaries as he did four years ago, but he remained heavily dependent on the ballots of blacks, who provided him with two-thirds of his 6.6 million votes this year. Gov. Michael S. Dukakis, whose campaign has stressed his immigrant roots, translated this into overwhelming support among Roman Catholics and Jews. … Mr. Dukakis won fewer than 200,000 black votes …
Another reader makes a better case:
In 2008, there had never been a black president before, and given our country's ugly history of racism, it was something worth rooting for, whether you liked Obama or not. Furthermore, my sense is that black voters weren't blindly supporting Obama simply because he'd be the first black president (otherwise, why didn't they come out in droves for Al Sharpton, or Carol Moseley Braun, or Alan Keyes?), but factoring it into their decision, which is perfectly legitimate.
Similarly, we've never had a Mormon president before; we've had 42 Protestants and 1 Catholic. If Romney wins the presidency this fall, even though I'll be disappointed for political reasons, I'll be cheering the fact that yet another barrier to the office has been shattered, and I perfectly understand why Mormon voters would be animated by this consideration.
Reminder for your reader aghast at the prospect of tribalism: American politics has always been tribal.
If you take an American citizen in 1840 or 1850, you could in many cases predict voting patterns by last name – a McCarthy or a Heinstadt, Irish and German Catholics respectively, are overwhelmingly likely to vote for Jackson and the Democrats. It's not so easy with straight-up English names like Smith or Chase, but add religion (or lack thereof) to the picture, and it gets clearer: the non-religious and the secular Smith or Chase go for the Jacksonian Democrats, while members of more evangelical and emotional sects caught up in the Second Great Awakening of the 1830s-40s are overwhelmingly Whig (and anti-immigrant) in their political views.
You could do this kind of break-down on literally every American political era, even in the colonial legislatures. Madison even accounts for this in Federalist No. 10, in which he proposes the then-novel idea that a giant republic would paradoxically be more stable than a smaller one, the various factions perpetually checking one another.