Glenn Greenwald makes an important point about the president's endorsement of same-sex marriage:

[T]he pressure continuously applied on Obama by some gay groups, most gay activists, and (especially) rich gay funders undoubtedly played a significant role....As David Sirota explained today, this demonstrates why it is so vital to always apply critical pressure even to politicians one likes and supports, and conversely, it demonstrates why it is so foolish and irresponsible to devote oneself with uncritical, blind adoration to a politician, whether in an election year or any other time (unconditional allegiance is the surest way to render one's beliefs and agenda irrelevant). When someone who wields political power does something you dislike or disagree with, it's incumbent upon you to object, criticize, and demand a different course. Those who refuse to do so are abdicating the most basic duty of citizenship and rendering themselves impotent.

It may very well be true that Obama took this step not out of any genuine conviction, but because he perceives that high levels of enthusiasm among the Democratic base generally and gay donors specifically are necessary for his re-election, or because Biden's comments forced his hand, or any number of other tactical reasons. I don't know what his secret motives are, but even if they could be discerned, I think it's irrelevant.

When it comes to assessing a politician, what matters, at least to me, are actions, not motives. If they do the wrong thing, they should be criticized regardless of motive; conversely, if they do the right thing, they should be credited. I've had zero tolerance over the last three years for people who pop up to justify all the horrible things Obama has done by claiming that he is forced to do them out of political necessity or in cowardly deference to public opinion; that's because horrible acts don't become less horrible because they're prompted by some rational, self-interested political motive rather than conviction. That's equally true of positive acts...

As I've said more than once, I'm less interested in electing officials who agree with me than in building movements that can pressure officials who don't agree with me. From January 2009 til yesterday, the president of the United States almost certainly agreed with the supporters of gay marriage but he wasn't willing to say so in public, thanks to the potential pressure to be felt from the other side. Then gay-rights activists organized some pressure of their own, and they got results.

You might retort that the activists haven't won much: Obama personally supports their right to marry but still favors a state-by-state approach to the issue. And even if you think the state-by-state approach is best, you can nod your head when Radley Balko points out the skewed priorities implicit in the president's on-again, off-again approach to federalism: "Obama apparently believes the states should be able to discriminate when it comes to marriage benefits, but if they allow cancer and AIDS patients to smoke pot, he asserts the supremacy of federal law, and sends in the SWAT teams."

Fine: It isn't a big victory. But it's a victory, and it's a lesson in how victories are often achieved -- one that activists around other issues, such as the drug war, can learn from. At any rate, with gay marriage the most important battleground has always been the culture, not the government. The shift in the president's public position might not change the law of the land, but it's a high-profile moment in the culture war.