U.S. Sen. Tammy Baldwin, D-Wis., the country's first openly gay senator, watched as the Supreme Court debated the future of the Defense of Marriage Act.
The 1996 law bars federal recognition and benefits for legally married same-sex couples.
Plaintiff Edith Windsor sued after getting a $363,000 estate tax bill, when her partner of 44 years died.
If Windsor had been married to a man, her estate tax bill would have been zero.
The Obama administration declined to defend DOMA in court, siding instead with the plaintiff in the case.
So House Republicans hired an attorney to defend the law.
Baldwin said she's hopeful the law will change.
"The march to full equality has been a long one in the United States for various groups of people, and this is another chapter," Baldwin said.
Baldwin said that she's heard from many Wisconsinites whose views on marriage equality have changed as they learn more about friends and family who they say are just like them.