(CNN) -- The U.S. Supreme Court on Wednesday heard arguments on the constitutionality of the 1996 Defense of Marriage Act, which defines marriage as only between a man and a woman.
The federal law means federal tax, Social Security, pension, and bankruptcy benefits, and family medical leave protections do not apply to gay and lesbian couples.
Wednesday's session came a day after the court heard arguments over California's Proposition 8, which defines marriage for that state as being between only a man and a woman.
The overriding question in that case is whether the Constitution's guarantee of equal protection under the law prevents states from defining marriage.
Here's the latest on Wednesday's Supreme Court session on the Defense of Marriage Act:
[Updated at 1:20 p.m. ET]
"I'm very optimistic that DOMA will be struck down. It has no rational basis for being," House Minority Leader Nancy Pelosi said just now. Pelosi was at the Supreme Court to hear arguments over DOMA and California's Proposition 8 over the past two days.
Pelosi's district has been at the epicenter of gay rights for decades. She called the oral arguments at the Supreme Court "thrilling."
[Updated at 1:01 p.m. ET]
According to CNN Supreme Court Producer Bill Mears, the court appeared divided along ideological lines about whether DOMA is discriminatory and steps on state marriage laws for gays and lesbians.
If legally married homosexuals were being denied more than 1,100 federal benefits, "What kind of marriage is that?" asked Justice Ruth Bader Ginsburg. She said the discriminatory effect was "pervasive."
But when Windsor's lawyer argued in court there was a "sea change" afoot today in support of same-sex marriage that leaves DOMA outdated, Chief Justice John Roberts said that was because of "the political effectiveness of those on your side" swaying public opinion.
Roberts and Justice Antonin Scalia suggested DOMA could still remain in place as a valid extension of congressional authority. Forty-one states do not allow same-sex marriage.
The potential swing vote, Justice Anthony Kennedy, said DOMA presents a "real risk of running into traditional state police power to regulate marriage."
[Updated at 12:54 p.m.]
The case of DOMA plaintiff Edie Windsor originated in New York, where Donna Lieberman heads the New York Civil Liberties Union.
"My state, the state of New York, respects the rights of all couples, straight or gay, to marry," Lieberman told reporters just moments ago. "But as long as DOMA remains on the books, the marriages are not truly equal. The federal government treats New York gay and lesbian couples as if they don't exist. ... It's time the federal government treats the marriages of all New Yorkers with the respect and dignity ... they deserve."
The federal government "should never relegate the marriage of a couple like Edie and Thea to the legal status of strangers," she said.
[Updated at 12:43 p.m. ET]
Marriage is a magic word, Windsor says, for anyone who doesn't understand why she still wanted to get married at age 73 to her partner, Thea Clara Spyer.
"I felt very serious" in court today, she says.
How does she think the oral arguments went? "I think it went beautifully. I think the justices were gentle, if I can use that word. They were direct, they asked all the right questions - but I didn't feel any hostility. ... I think it's going to be good."
[Updated at 12:41 p.m. ET]
Windsor takes the mic and says, "Today, I'm an out lesbian who just sued the United States government. It's a little overwhelming."
[Updated at 12:37 p.m. ET]
Windsor's attorney, Roberta Kaplan, told reporters just now: "Today's arguments tells the lesson of why it is we have a Constitution: to bind us together as citizens of one nation, all of whom guaranteed equal protection under the law. There is no one individual who personifies the concept of equal protection like Edie Windsor."
[Updated at 12:32 p.m. ET]
The plaintiff, Edie Windsor, is walking out and being greeted by cheering crowds. Alicia Keys' "Girl On Fire" is blasting from speakers.
[Updated at 12:29 p.m. ET]
"The court appears to be moving toward an out, if it wants it, on procedural grounds," CNN Correspondent Joe Johns said just minutes ago. At issue is whether House Republicans have standing to defend DOMA instead of the Obama administration, which has decided not to defend it.
As for the merits of the case, there was a lot of discussion as to why the U.S. Congress passed DOMA in 1996 -- whether it was just trying to ensure legal uniformity on marriage, or whether something else was afoot, like moral disapproval of homosexuality, Johns said.
[Updated at 12:22 p.m. ET]
"They are obviously very deeply split. But I think DOMA is in trouble," says CNN Senior Legal Analyst Jeffrey Toobin after watching the arguments.
[Updated at 12:20 p.m. ET]
Both parties are leaving the courthouse right now. Stay tuned for latest developments.
[Updated at 12:16 p.m. ET]
Oral arguments on the