The Supreme Court could be on the verge of a historic ruling striking down the federal Defense of Marriage Act — if, that is, the justices overcome their concerns about standing and jurisdiction.

Oral arguments Wednesday in United States v. Windsor revealed a court that, like the day before, wanted to proceed cautiously on such a hot-button issue. On Tuesday in Hollingsworth v. Perry,  justices’ concerns focused on the impact of same-sex marriage, a relatively new phenomenon, on society and children.

But in the Windsor case, the justices voiced more traditional concerns about whether the case could proceed at all under the constitutional requirement that the court decide only “cases and controversies” — given that the Justice Department is no longer defending DOMA, and a group of House members is standing in its place.

Plaintiff Edith Windsor of New York state, which recognizes same-sex marriages, challenged the 1996 law, which defines marriage as between a man and a woman for federal purposes. She claimed that in spite of her legally recognized marriage to a woman, Thea Spyer, the law required her to pay a federal estate tax that opposite-sex married couples don’t have to pay.

In 2011, the Obama administration announced it would no longer defend the statute in cases like Windsor’s. A Republican-led House group, called the Bipartisan Legal Advisory Group, intervened to defend the statute.

Allowing the House group to defend the law instead of the United States is “very strange,” in the words of Justice Sonia Sotomayor. Justice Antonin Scalia said courts should not decide cases “just for fun” when the original parties in litigation end up on the same side. And Chief Justice John Roberts Jr. said that asking the court to decide a case in which “all parties agree” is “something we’ve never done before.”

Nonetheless, it appeared that Deputy Solicitor General Sri Srinivasan made headway when he told the court it does have jurisdiction anyway, in part because the government has continued the appeal in spite of its stance on the law to show “respect” for Congress.

After 50 minutes of discussion of the standing issues, the court turned to the merits of whether the federal law violates “equal protection” guarantees by treating legally married same-sex couples differently than their opposite-sex counterparts.

Former solicitor general Paul Clement, now a partner at Bancroft, argued on behalf of the House Republicans that Congress is entitled to establish uniform rules for federal benefits — even if they differ from state definitions. By staying uniform across the nation, Clement said the law also has the benefit of keeping the federal government, “a big player,” out of the state-by-state debate over same-sex marriage.

Justice Ruth Bader Ginsburg immediately challenged Clement, asserting that the federal law has such a pervasive effect on taxes, Social Security and family leave, among other issues, that same-sex couples are entitled to wonder, “What kind of marriage is this?” Later, she said DOMA consigns states to offering “two kinds of marriage: real marriage and then this sort of skim milk marriage.”

Justice Anthony Kennedy, widely viewed as the pivotal vote, also said the pervasive nature and lure of federal benefits, denied by DOMA to legally married same-sex couples, poses “the real risk of running in conflict with what ha always been thought to be the essence of the state police power, which is to regulate marriage, divorce, custody.” Given the critical comments about DOMA made during oral argument by Justices Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan, Kennedy could provide a fifth vote to strike down the law.

After the argument was over Judith Schaeffer, vice president of the liberal Constitutional Accountability Center said, “A majority of justices today appeared to regard DOMA for what it is: a pervasive program of discrimination that changes 1100 laws and touches every aspect of life.”