In response to Herman Cain saying he would "leave it up to the states" to define marriage on Meet the Press, Jeff Anderson of The Weekly Standard proposes a way Cain could make good on his promise that he is fully pro-marriage:

...there’s a way for Cain [...] to elaborate on and to refine his answer in a manner that’s consistent with his support for traditional marriage, his support for federalism, and his response to Gregory. Cain could make clear that he’s in favor of constitutionalizing the Defense of Marriage Act (DOMA).

Cain [...] could emphasize that constitutionalizing DOMA would ensure that the people of each state actually would get to decide this issue for themselves. That result is now very much in doubt, as judges (who illegitimately thrust this issue forward in the first place by imposing their own policy preferences from the bench) could potentially require one state to accept the marital definition of another, under a dubious reading of the Constitution’s Full Faith and Credit clause (Article IV, Section 1) or even the Equal Protection clause (Amendment XIV). At the same time, constitutionalizing DOMA would ensure that, within its own sphere of operations, the federal government would adhere to the traditional and time-honored definition of marriage.

Or, Cain could simply sign the NOM marriage pledge, which among other things would commit him to supporting a federal marriage amendment while rigorously defending DOMA.