(CNN) -- New York City Mayor Michael Bloomberg, who favors a proposed national ban on semi-automatic firearms modeled after military assault weapons, said Thursday that the American public will watch closely how U.S. senators vote on the issue. "The rest of us will have to decide how they feel about (senators) and their stands," Bloomberg said at a news conference with Vice President Joe Biden. The ban could come up as a proposed amendment to a larger gun-control measure this spring.