Jacob Sullum is a senior editor at Reason.com and a nationally syndicated columnist:

Last month, when President Obama finally endorsed gay marriage after years of equivocation, he emphasized that he still thinks states should be free to address the issue as they see fit. Since many voters strongly oppose gay marriage, it is clear why Obama advocates a federalist approach to the question. But it is not clear that he logically can.

... Obama does not argue that DOMA violates the 10th Amendment by impermissibly intruding on a power that the Constitution reserves to the states. Instead he says the law violates the guarantee of equal protection implicit in the Fifth Amendment's Due Process Clause.

... In fact, [DOJ's] Holder and Obama implicitly have staked out a stronger position against state bans on gay marriage than the 9th Circuit did. Under the heightened scrutiny favored by Obama, the government must show that a legal distinction based on sexual orientation is "substantially related to an important government objective."

... many other states' gay marriage bans could be vulnerable under the heightened scrutiny that Obama applied to DOMA.

Obama may wish to avoid the implications of his constitutional logic until after the presidential election. But if the Supreme Court agrees to hear the California case this fall and asks the solicitor general to weigh in, that may not be possible.