The utter cynicism and frivolity of the Obama administration is nowhere more evident than in Attorney General Eric Holder’s announcement that he and the president have decided that the Department of Justice will no longer defend the constitutionality of the Defense of Marriage Act (DOMA). The announcement is an outrage not only because of the result it reaches, but also because of the constitutional wreckage it leaves in its wake.

That wreckage is both substantive and structural. Obama and Holder reason that the statute violates the “equal-protection component” of the Due Process Clause of the Fifth Amendment, which applies to the …