In an omen to both sides of the same-sex marriage debate that they risk walking away with less than they want, arguments before the Supreme Court went from yesterday’s debate on whether a state’s voters can usurp what the federal government may deem a constitutional right to today’s issue of whether the federal government can have a Defense of Marriage Act if the business of marriage should be the prerogative of the states.

“The question is whether or not the federal government under our federalism scheme has the authority to regulate marriage,” said Justice Anthony Kennedy, a potential swing vote in today’s case and in the arguments against California’s Proposition 8 heard yesterday.

“What gives the federal government the right to be concerned at all about what the definition of marriage is?” Justice Sonia Sotomayor asked.

Nine states currently recognize gay marriage and 30 states have banned it via constitutional amendments.

United States v. Windsor is an appeal on a case brought by Edie Windsor, who married her partner in Canada in 2007. When her partner died in 2009, their home state of New York recognized same-sex marriages performed elsewhere. When Windsor inherited her spouse’s estate, she was forced to pay $363,000 in taxes on the inheritance because her marriage was not recognized on a federal level.

Because of the core tax issue, many felt the conservatives on the court would be more sympathetic to the case despite the highly charged facet of gay marriage.

“Suppose we look just at the estate tax provision that’s an issue in this case, which provides specially favorable treatment to a married couple, as opposed to any other individual or economic unit. What was the purpose of that? Was the purpose of that really to foster traditional marriage?” asked Justice Samuel Alito. “Or was Congress just looking for a convenient category to capture households that function as a unified economic unit?”

Attorney Paul Clement, a former solicitor general who led the challenge to ObamaCare last year, argued that Congress passed DOMA in 1996 faced with “the prospect that one state, through its judiciary, will adopt same-sex marriage and then, by operation of the full faith and credit law, that will apply to any — any couple that wants to go there.”

“And so Congress is worried that people are going to go there, go back to their home jurisdictions, insist on the recognition in their home jurisdictions of their same-sex marriage in Hawaii, and then the federal government will borrow that definition, and, therefore, by the operation of one state’s state judiciary, same-sex marriage is basically going to be recognized throughout the country,” Clement said.

“And what Congress says is, wait a minute. Let’s take a timeout here. This is a redefinition of an age-old institution. Let’s take a more cautious approach, where every sovereign gets to do this for themselves.”

“You’re saying, we can create this special category — men and women — because the states have an interest in traditional marriage that they’re trying to protect,” Sotomayor interjected. “How do you get the federal government to have the right to create categories of that type based on an interest that’s not there, but based on an interest that belongs to the states?”

“One way to stay out of the debate and let just the states develop this and let the democratic process deal with this is to just say, look, we’re going to stick with what we’ve always had, which is traditional definition,” Clement argued. “We’re not going to create a regime that gives people an incentive and point to federal law and say, well, another reason you should have same-sex marriage is because then you’ll get a state tax deduction.”

“It’s not as though, well, there’s this little federal sphere and it’s only a tax question,” said Justice Ruth Bader Ginsburg. “It’s as Justice Kennedy said, 1,100 statutes, and it affects every area of life. And so you’re really diminishing what the state has said is marriage.”

Justice Elena Kagan noted that a House report said Congress “decided to reflect and honor a collective moral judgment and to express moral disapproval of homosexuality” in its passage of DOMA.

“Does the House report say that? Of course the House Report says that. And if that’s enough to invalidate the statute, then you should invalidate the statute,” Clement responded. “…The House report says some things that we are not — we’ve never invoked in trying to defend the statute. But the House report says other things, like Congress was trying to promote democratic self-governance.”