He added: "Are we really prepared to say that we're powerless in the face of such carnage, that the politics are too hard? Are we prepared to say that such violence visited on our children year after year after year is somehow the price of our freedom?"
Sen. Chuck Schumer, D-N.Y., said the nation "could be at a tipping point ... a tipping point where we might actually get something done" on gun control. He and other Democrats, as well as Lieberman, said they want to ban the sale of new assault weapons and make it harder for mentally ill individuals to obtain weapons. Lieberman said a new commission should be created to look at gun laws and the mental health system, as well as violence in movies and video games.
"Assault weapons were developed for the U.S. military, not commercial gun manufacturers," Lieberman said before the Newtown vigil Sunday night.
"This is a moment to start a very serious national conversation about violence in our society, particularly about these acts of mass violence," said the Connecticut senator, who is retiring at the end of the year.
Sen. Dianne Feinstein, D-Calif., said she will introduce legislation next year to ban new assault weapons, as well as big clips, drums and strips of more than 10 bullets.
"It can be done," Feinstein told NBC's "Meet the Press" of reinstating the ban despite deep opposition by the powerful National Rifle Association and similar groups.
Bloomberg said Obama could use executive powers to enforce existing gun laws, as well as throw his weight behind legislation like Feinstein's.
"It's time for the president, I think, to stand up and lead and tell this country what we should do — not go to Congress and say, 'What do you guys want to do?'" Bloomberg said."