Feinstein said those Democrats with concerns about the legislation needed to ask themselves what their silence would mean.
"Sandy Hook is more eloquent testimony than any of us could possibly give," she said. "If members of this body are so insensitive to what happened to those small bodies from that Bushmaster when it all becomes known, America is hopeless."
Even some of Feinstein's supporters believe the assault weapons ban is so unattainable politically that the focus should be on other measures that might even be more effective policy.
Vice President Joe Biden said Thursday that he's more concerned about limiting the number of rounds in a gun magazine than about banning assault weapons that account for a small percentage of gun deaths.
Biden argued that the shooter at the Sandy Hook Elementary School in Newtown, Conn., could have been slowed down if he had fewer rounds in each magazine and had to change clips more often. "Maybe if it took longer, maybe one more kid would be alive," Biden said during an online video chat on Google Plus.
The vice president led a White House gun control task force in the wake of the Newtown shooting last month.
Biden is launching the White House's promotional tour on gun control Friday with a trip to Virginia, a state that has experienced its own school shooting tragedy yet maintains an avidly pro-gun tradition. His office said Biden will hold a round-table discussion in Richmond with experts who worked on gun safety following the 2007 shooting at Virginia Tech.