The Newtown massacre prompted a national debate over gun laws and spurred Obama to prioritize the issue for the first time.
"Sometimes you pick the time; sometimes the time picks you," Duncan said. "Sadly, the time has picked us. And I'm just convinced that as a country, if we don't move forward in a thoughtful way to do something to protect our babies, it will never happen."
In January, Obama and Biden announced what would be the most far-reaching overhaul of gun laws in generations. They are pressing for universal federal background checks, as well as bans on assault weapons and high-capacity ammunition magazines.
Since then, Obama, Biden and other senior administration officials have traveled the nation to rally public support around their proposals.
Meanwhile, Connecticut Gov. Dan Malloy, a Democrat, announced state-level proposals Thursday for universal and comprehensive background checks for gun buyers, a ban on high-capacity ammunition magazines and steps to strengthen Connecticut's assault weapons ban.
"We run a risk of letting this critical moment in history pass," Malloy said. "None of us want that to happen, and none of us should let it happen."