Gay marriage moved one step closer to the Supreme Court yesterday when the U.S. Court of Appeals for the First Circuit ruled the Defense of Marriage Act (DOMA) unconstitutional.

DOMA was signed into law by President Bill Clinton in 1996.  It legally defines marriage as between one man and one woman, and permits states to refuse to recognize the validity of same-sex marriages performed in other states.  In addition, Section 3 of the law specifies that same-sex marriages will not be recognized for federal purposes–including insurance benefits for government employees, Social Security survivors’ benefits and the filing of joint tax returns.

It was Section 3 of DOMA that the appeals court found unconstitutional.  From the opinion:

“To conclude, many Americans believe that marriage is the union of a man and a woman, and most Americans live in states where that is the law today. One virtue of federalism is that it permits this diversity of governance based on local choice, but this applies as well to the states that have chosen to legalize same-sex marriage. Under current Supreme Court authority, Congress’ denial of federal benefits to same-sex couples lawfully married in Massachusetts has not been adequately supported by any permissible federal interest.”

The court did not address the issue of states’ recognition of same-sex marriages performed in other states.  The unanimous ruling, 3-0, with two judges having been appointed by Republican presidents, was stayed until the Supreme Court hears the issue.

Two Massachusetts cases and a California class action suit by public employees have also found Section 3 unconstitutional.  Furthermore, in February the Ninth Circuit Court of Appeals held in Perry v. Brown that California’s Proposition 8 outlawing gay marriage is unconstitutional.  With cases accruing in the lower courts, it is inevitable that the Supreme Court will decide a gay marriage case, likely in its next term, which begins in about four months.  Which begs the question: what will the Justices say?

Their decision likely rests with Justice Anthony Kennedy, the Court’s ‘swing’ vote, who has previously endorsed gay rights.  Kennedy authored the opinions in two landmark cases, Romer v. Evans, which overturned a ban on LGTB discrimination laws, and Lawrence v. Texas, which overturned state sodomy laws.

As supportive as Kennedy is of gay rights, he is also a cautious jurist, so he is unlikely to issue the opinion gay marriage advocates would most like, that marriage is a fundamental right under the 14th Amendment’s Equal Protection Clause.  The Court tends to track, rather than buck, public opinion, and with polls indicating that about half of Americans support gay marriage and President Obama expressing his approval, the possibility exists that the Court could endorse full marriage rights, but this is still improbable.

The most cautious choice would be for the Court to rule precisely as the First Circuit did: that Section 3 of DOMA, which prevents gay couples married in states such as New York or Massachusetts from receiving federal benefits or filing joint tax returns, is unconstitutional.  This would be a very narrow holding, delivering full equality under the law to those in states where gay marriage is legal, but bringing absolutely no change in states where it is banned.

A third option – proposed by Mae Kuykendall in The New York Times last week – is for the Supreme Court to find Section 3 of DOMA unconstitutional, as well as rule that states must recognize gay marriages performed in other states.  This would effectively legalize gay marriage throughout the country, as a couple from, say, Pennsylvania could travel to New York to get married and then return home with their marriage officially recognized by their state and the federal government.  States would still have the prerogative to not sanction gay marriage within their borders, however.

Legal momentum has clearly shifted in favor of gay marriage, and so it is likely that gay marriage advocates will be hearing good news from the Court soon – how good is the real question.