Since the April defeats for traditional marriage in the Iowa Supreme Court, the Vermont Legislature and the Washington, D.C., City Council, Americans in the other 48 states are quietly stress-testing their legal defenses against the spread of legalized same-sex marriage.

The Iowa ruling was particularly shocking. Not one of Iowa's seven supreme court justices, who were appointed by both Republican and Democratic governors over the past 15 years, could identify a valid public purpose for the institution that has guided our civilization for thousands of years.

The unanimity of the decision sets Iowa apart from the seven other states -- Massachusetts, Washington, New York, New Jersey, Maryland, Connecticut, and California -- where state supreme courts have ruled on same-sex marriage since 2003. A majority of the more than 50 state supreme court justices in those seven states had no trouble recognizing the value of conferring public recognition and benefits on the union of husband and wife, as also did lower court judges in Indiana and Arizona.

Unlike the 30 states that added language to their state constitutions supporting the traditional definition of marriage, Iowa does not allow citizen initiatives to go directly to the ballot. The leaders of both houses of the state legislature have refused to allow their members to vote on a marriage amendment, so Iowans now have the difficult task persuading legislators to bypass their own leaders in order to schedule a vote on a measure that polls show two-thirds of Iowans support.

However, a much more critical legal drama began last month in a federal court in Boston. The same law firm that brought gay marriage to Massachusetts is trying to overturn the federal law that protects the traditional definition of marriage in all federal departments, agencies and programs. Left-wing Harvard professor Laurence Tribe praises this lawsuit as a "surgical attack on DOMA," a law he calls "particularly invidious."

The federal Defense of Marriage Act (DOMA) -- signed by President Bill Clinton in 1996 after an overwhelming bipartisan vote in Congress (342-67 and 85-14) -- provides that federal laws must be interpreted in accord with the traditional definition of marriage as the union of husband and wife.

Five years ago, the Government Accountability Office (GAO) counted 1,138 federal laws that refer to marriage, spouse, husband or wife, and DOMA requires these laws to be administered uniformly throughout the nation. DOMA requires that even in states where same-sex unions are recognized, their partners are not recognized as married for purposes of federal law. Continued...