Several moderate Democrats are holding back as they assess the political landscape. They're also waiting to see exactly what the Senate will consider.
Sen. Mark Begich, D-Alaska, said Wednesday his state's voters tell him, "Don't take away our rights, our individual rights, our guns." Begich said he opposes a strict proposal requiring background checks for nearly all gun sales but will wait to see whether there is a bipartisan compromise he can support.
The problems faced by gun control supporters go beyond the challenge of winning over moderate Democrats. GOP opponents are sure to force Democrats to get 60 of the Senate's 100 votes to win, and there are only 53 Democrats plus two independents who generally support them.
Also targeted by Bloomberg's ads are 10 Republicans, including Sen. Jeff Flake of Arizona, home of ex-Rep. Gabrielle Giffords, who was severely wounded in a mass shooting; the retiring Sen. Saxby Chambliss of Georgia; and moderate Sen. Susan Collins of Maine.
In another indicator of hurdles facing gun control forces, the Senate voted 50-49 last week to require 60 votes for any legislation narrowing gun rights. The proposal lost because 60 votes in favor were required, but six Democrats voted for the proposal, offered by conservative Sen. Mike Lee, R-Utah.
"It confirms there's no such thing as an easy gun vote," said Jim Kessler, a senior vice president of the centrist Democratic group Third Way.
Underscoring the uncertainty about moderate Democrats:
—Sen. Mark Warner, D-Va., is "still holding conversations with Virginia stakeholders and sorting through issues on background checks" and proposals to ban assault weapons and high capacity ammunition magazines, spokesman Kevin Hal said.
—Pryor said of Bloomberg's ads: "I don't take gun advice from the mayor of New York City. I listen to Arkansans." Spokesman Michael Teague said Pryor opposes universal background checks but could favor expanding the requirement to gun show sales.