Andrew Koppelman thinks Jack Balkin is wrong:
Judge Tauro’s opinions invalidate DOMA on two grounds: it invidiously discriminates against same-sex couples in violation of the Equal Protection Clause of the Fourteenth Amendment, and it invades states’ prerogative to define marriage in violation of the Tenth Amendment. Jack correctly observed, in this blog and in statements quoted in a front page story in the New York Times, that the second of these is a lousy argument with mischievous implications. But the bad argument is surplusage. The Equal Protection argument is enough to invalidate the law.
Balkin clarifies and corrects.