Washington (CNN) New Jersey Sen. Cory Booker had a response Sunday for former Vice President Joe Biden after his 2020 competitor expressed some skepticism earlier this week about Booker's proposal for a federal gun licensing system.

"There are states that have done this that have seen precipitous drops in gun violence," Booker said Sunday on CNN's "State of the Union." "We need to start looking at the things that work."

Speaking on the heels of a recent mass shooting at Virginia Beach that left a dozen dead, Booker said his previously announced set of gun control proposals would lower gun violence in the US overall and his call for a federal licensing system will take on the high level of gun violence in America.

When asked about the proposal while campaigning in New Hampshire, Biden said he was not sure the policy was doable under the Constitution, but also that it might not be effective.

"I think there's a lot of things we can do directly now," Biden said. "That's not going to change, gun licensing will not change whether or not people buy what weapons -- what kinds of weapons they can buy, where they can use them, how they can store them."

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