Today we learned that Barack Obama opposes the proposed amendment to the California constitution defining marriage as the union of a man and a woman. In a letter to a gay civil rights group in San Francisco, Obama said he rejects "the divisive and discriminatory efforts to amend the California Constitution" and similar efforts in other states.

At the same time, Obama has repeatedly said that while he supports civil unions for gay couples he believes marriage is between a man and a woman. At a Democratic debate last August sponsored by the gay-themed cable station LOGO, he had this exchange with Human Rights Campaign Executive Director Joe Solmonese:

MR. SOLMONESE: So to follow up on your point about the state issue, if you were back in the Illinois legislature where you served and the issue of civil marriage came before you, how would you have voted on that?

SEN. OBAMA: Well, I — you know, my view is that we should try to disentangle what has historically been the issue of the word "marriage," which has religious connotations to some people, from the civil rights that are given to couples, in terms of hospital visitation, in terms of whether or not they can transfer property or any of the other — Social Security benefits and so forth. So it depends on how the bill would've come up.

I would've supported and would continue to support a civil union that provides all the benefits that are available for a legally sanctioned marriage.

Though the answer was a bit muddled, and seems calculated to ease the blow of his opposition to gay marriage in front of a gay audience, I read this to mean that Obama would oppose a bill in a state legislature to permit same-sex couples to marry but would support a bill to let these same couples enter civil unions giving them equivalent rights under state and federal law. This has become the dominant view of the Democratic Party. (If in fact he personally opposes gay marriage but supports it as a matter of public policy, his campaign hasn't said so.)

Assuming that Obama's opposition to gay marriage is not simply "personal," but is also a matter of public policy, I find Obama's current position perplexing. He opposes a referendum that would simply enshrine his purported public-policy view that marriage is between a man and a woman because, he says, it is "discriminatory."

But how is the proposed amendment any more "discriminatory" than his own position? His position is that marriage is between a man and woman; the proposed amendment says that marriage is "between a man and a woman." (Full text: "Only marriage between a man and a woman is valid or recognized in California.”) The proposed California amendment is narrower than the other proposed state constitutional amendments, many of which have explicitly bitten off much more than gay marriage.

Is there any way to reconcile opposition to gay marriage with opposition to the California amendment? I can think of three ways to reconcile these views, none of which is cited by the Obama campaign.

First, I suppose one could oppose writing the definition into the state constitution as opposed to state statutes. This would leave the state legislature and governor with the flexibility and the power to make the call at a later time. But the problem with that is that the state supreme court effectively wrote the new definition into the state constitution, removing this very power from the state legislature and the governor. If you oppose gay marriage on policy grounds, there is now no way to implement your view except to constitutionalize it by amendment. The state supreme court has left you no choice. And in California, because it's so easy to amend the state constitution, you're free to vote for a repeal at a later date if you change your mind on this issue. And you don't have to worry in 2008 that you are helping to set up a supermajority barrier to the possibility that you will change your position in the future.

Second, since gay marriages are a fait accompli for the next few months, even if you oppose them you might not want to reverse the interim marriages (which is a possible effect of passing the amendment) or, more abstractly, "take away rights." These would be incredibly generous reasons for a real opponent of gay marriage to oppose the California amendment since the number of interim marriages will be small in absolute terms, the marriages exist only by mandate of four judges, they are entered with full knowledge and notice that they may be nullified in a short time, and the cost of losing the referendum will be many more such marriages into the indefinite future. But if Obama is such an anti-SSM altruist, he does not give this as a reason for opposing the amendment.

Third, a gay-marriage opponent who supports civil unions (like Obama) could vote against the California amendment on the ground that it might also be interpreted to eliminate the state's domestic partnership system. This might be an unacceptably high cost if you oppose gay marriage, but don't oppose it very strongly, and think the costs of ending the domestic partnership system would be high. I think it unlikely the amendment will be interpreted so broadly by the California courts if it passes, but the risk is above zero. However, once again, Obama does not offer this as a reason to oppose the amendment.

So what's really going on? I think there are two things happening. First, I don't think Obama really opposes gay marriage deep down and I suspect he does see the exclusion of gay couples as a kind of discrimination. He has never been able to explain his reasons for opposing gay marriage — which is very revealing for a man who's otherwise unusually thoughtful. He just says, basically, I oppose gay marriage "because I say so." So calling the amendment discriminatory and divisive may be candor squeaking through. Second, and probably more importantly, this is an instance where politics necessitates cognitive dissonance. Gays and those who support gay equality are a critical constituency in the Democratic Party. Obama can't keep the gay-friendly base happy and support the amendment, which is rightly seen by them as involving huge stakes for the gay-marriage movement. But at the same time he has calculated that he can't come out for gay marriage as a matter of public policy because that might mean losing the election.

Don't get me wrong, I strongly oppose the California amendment and intend to contribute to its defeat. And on one level, I am very gratified by Obama's opposition. It might actually help sway some of his socially conservative black and Latino supporters, who will vote in large numbers in California in November. But then, I support gay marriage. If I opposed it, I'd probably be either mystified or angered.

Obama's explanation for why he opposes gay marriage and opposes the proposed California amendment banning it can't be squared as a matter of logic. It's a matter of politics, which says something about how much things have changed in a short time. We've gone from the Democratic presidential nominee in 2004 opposing gay marriage and supporting state constitutional amendments to ban it (as Kerry did, even where gay marriage existed, in Massachusetts); to a Democratic nominee who says he opposes gay marriage, but who's uncharacteristically at a loss to explain himself, and who opposes the only way to prevent it from becoming a reality in a state with 40 million people; to, I predict, a nominee in 2012 or 2016 who will say he or she personally favors gay marriage but says the president has no role in the decision because this is an issue that should be left to the states.