"You can repeal it," he said. "We repealed prohibition."
Molly Smith, the artistic director of Washington's Arena Stage, and her partner organized the march. Organizers said that, in addition to the 100 people from Newtown, buses of participants traveled from New Jersey, New York and Philadelphia. Others flew in from Seattle, San Francisco and Alaska, they said.
While she's never organized a political march before, Smith said she was compelled to press for a change in the law. The march organizers support Obama's call for gun-control measures. They also want lawmakers to require gun safety training for all buyers of firearms.
"With the drum roll, the consistency of the mass murders and the shock of it, it is always something that is moving and devastating to me. And then, it's as if I move on," Smith said. "And in this moment, I can't move on. I can't move on.
"I think it's because it was children, babies," she said. "I was horrified by it."
After the Connecticut shootings, Smith began organizing on Facebook. The group One Million Moms for Gun Control, the Washington National Cathedral and two other churches eventually signed on to co-sponsor the march. Organizers raised more than $50,000 online to pay for equipment and fees to stage the rally, Smith said.
Lawmakers from the District of Columbia and Maryland rallied the crowd, along with Marian Wright Edelman of the Children's Defense Fund and Colin Goddard, a survivor from the Virginia Tech massacre.
Goddard said he was shot four times at Virginia Tech and is motivated to keep fighting for gun control because what happened to him keeps happening -- and that nothing's been done to stop it.
"We are Americans," he said, drawing big cheers. "We have overcome difficulties when we realize we are better than this."
Smith said she supports a comprehensive look at mental health and violence in video games and films, but she said the mass killings at Virginia Tech and Aurora, Colo., and Newtown all began with guns.
"The issue is guns. The Second Amendment gives us the right to own guns, but it's not the right to own any gun," she said. "These are assault weapons, made for killing people."