Dr. John Eastman, NOM's Chairman, is inside the Supreme Court again today for the oral arguments in the Defense of Marriage Act cases.
Today he explains in US News & World Report why DOMA isn't mandated by the Due Process clause:
Those seeking to redefine marriage into a genderless institution must be pessimistic about their chances before the Supreme Court, because they are doing everything they can to prevent the Court from deciding whether the traditional definition marriage, as expressed in the Defense of Marriage Act, is unconstitutional. The Department of Justice refused to defend the statute, despite the fact that it was overwhelmingly passed by bipartisan majorities in Congress and signed into law by President Clinton just a decade and a half ago. It now seeks to prevent the House of Representatives from defending the statute, so that the Court would not even have jurisdiction to hear the case.
But existing precedent is pretty clear—the Department can't deprive the Supreme Court of jurisdiction merely by refusing to do its duty and defend an Act of Congress; in such circumstances, Congress itself can intervene to defend a statute it passed.