In the wake of a horrific massacre at an elementary school in Connecticut, Sen. Diane Feinstein (D-CA) is vowing to introduce a bill to ban assault weapons when the Senate reconvenes next month.

During a panel segment on Sunday, NBC's David Gregory asked Feinstein if President Barack Obama had failed to lead on gun control.

"I can tell you that he is going to have a bill to lead on, because of this first day bill I'm going to introduce in the Senate and the same bill will be introduced in the House – a bill to ban assault weapons," the California Democrat replied. "It will ban the sale, transfer, the importation and the possession, not retroactively, but prospectively. And it will ban the same for big clips, drums or strips of more than ten bullets. So there will be a bill. We've been working on it now for a year."

"We tried to take my bill from '94-2004 and perfect it. We believe we have. We exempt over 900 specific weapons that will not fall under the bill. But the purpose of this bill is to get just what Mayor [Michael] Bloomberg said, weapons of war off the streets of our cities."

Feinstein added that she expected the president to get behind the legislation.

"We'll be prepared to go and I hope the nation will help," she said.

Watch this video from NBC's Meet the Press via Video Café, broadcast Dec. 16, 2012.