Last week, the Justice Department filed a motion to dismiss a lawsuit by a married same-sex couple from California. The suit by Arthur Smelt and Christopher Hammer sought to invalidate the Defense of Marriage Act ("DOMA"), a federal law enacted in 1996 that has two key provisions: Section 2 authorizes states that do not themselves permit same-sex marriage to deny recognition to legal same-sex marriages performed in other states; and Section 3 defines marriage for purposes of federal law as encompassing "only a legal union between one man and one woman as husband and wife."...