The usual expectation of the Justice Department when a federal law is being challenged in court is to defend the law, as long as some good-faith argument can be mustered in its defense, even if the administration in power at the moment disagrees with the law on policy grounds. The Obama Administration has chosen not to defend the Defense of Marriage Act (DOMA), a law that it had been defending with what it had taken to be good-faith arguments for most of the Obama presidency.
The president's change of heart on this issue isn't just a question of consistency between his past statements (including what he ran his campaign on) and his current views, because it's possible to change your mind on important issues. It also isn't just about whether the solicitor general always has to defend policies that the sitting president disagrees with. There are plenty of cases of other presidents choosing not to defend laws that are challenged in court.
What especially worries me about this current move is that there are people on both sides of the issue who do have good-faith arguments. They each believe there are convincing arguments. The Obama Administration acknowledged this by presenting those arguments. They seem to have gotten tired of offering arguments they no longer agree with (on the more charitable explanation: I would say "or have been politically pressured to abandon" on the less charitable explanation). Barack Obama was convinced enough by such arguments, if we take him to be remotely honest, that he defended the law during his run for the White House. He directed his solicitor general, who is now his second Supreme Court appointee, to defend the law in the courts. But if he's supposed to defend the law unless he thinks there are no good-faith arguments for it, that means he implicitly has indicated that he (no longer?) thinks there are good faith arguments for it.
I've been thinking about the implications of this, in light of one of the key themes that got him elected. He talks about putting yourself in the shoes of your political opponent, thinking how they think, coming to understand them so that you don't simply present them as evil incarnate. They differ from you on policy matters, but it's often based on core values that we all share, just applied differently (and in your own view incorrectly). In other words, he spends quite a lot of energy calling on people to do politics differently, in a way that recognizes they have good-faith arguments for their positions.
Now this isn't the first place where I see a conflict between that message, which is a major theme of his book The Audacity of Hope, and how he actually describes his political opponents when disagreeing with them, which strikes me as not abiding by his own advice. I could give numerous examples from that very book, but I don't have a hard copy from the library yet, so I'll have to come back to that at another time. (But see my discussions of his comments about Bush's Supreme Court picks for a clear example of this.)
I have to wonder if this is another example. By implicitly indicating that he doesn't think there are good-faith arguments for DOMA, is he therefore tarring all proponents of DOMA, including every member of Congress who voted for it (and it was a popular bill on the Democratic side) with having no good-faith arguments for the bill? They were all supporting it disingenuously, in other words. What would motivate them to support it if they had no good-faith reasons to support the law in principle? Presumably corruption, right? Is he asserting that of all supporters of DOMA, including the Senator Obama who ran for president in 2008 and succeeded in getting elected, who went on to instruct his Solicitor General Elena Kagan to defend the law with arguments he was claiming were good-faith arguments? The arguments often given about his inconsistency on this issue are too simplistic, given that people really can change their minds in good faith. Perhaps he has (though I admit some skepticism). But I'm not sure he can consistently claim that there's no good-faith argument without thereby admitting deception and political opportunism on his own part.
The only way out of this argument I can see is if he's going to insist that you can think there are good-faith arguments for a position but still refuse to defend it. But that does go against significant tradition, and it has him falling afoul of another problem he raises in his book, and that's the biggest criticism he thinks he has of the Republicans under Bush. He accuses them of being unwilling to abide by how things have traditionally been done. Some issues he picks on involve issues where he sees a constitutional violation. (On many of those issues, I suspect he's changed his mind and simply continued the Bush policy, since he mostly had in mind war on terrorism issues, where his policies haven't different much from Bush's.) One place he applies this is to the so-called "nuclear option" issue in the Senate, where he thought they should continue to allow the filibuster in judicial nominations, in part because it's a longstanding tradition. Now he's going against a significant tradition, if he thinks there are good-faith arguments, anyway.
So either way, he's going against a major theme in his book.