Pryor waited until almost the last minute to announce his decision on the background-check measure. "It's too broad, unworkable, and unreasonable for hunters and gun owners in our state," he said.
A writer for the political website Arkansas Blog said, even before Pryor cast his vote, it's "doubtful that he'll get credit from the gun zealots for siding with them."
The votes by Pryor, Baucus and Begich stand in contrast to those of two other Senate Democrats facing potentially tough races next year: Mary Landrieu of Louisiana and Kay Hagan of North Carolina. Both voted for the expanded background checks on gun buyers.
Hagan's and Landrieu's states have important characteristics lacking in their colleagues' states, according to Ferrel Guillory, a Louisiana native and director of the Program on Public Life at the University of North Carolina at Chapel Hill.
Landrieu's political base is in New Orleans, Guillory said, where her brother — like their father before them — is mayor, and where gun violence is a major problem. Landrieu may have little to gain by voting with the NRA.
"She's not going to get the middle-income, middle-age male voter," Guillory said, describing the typical Romney supporter. "She needs the newer electorate," he said, which includes younger voters, minorities and high-tech workers in cities such as Baton Rouge.
North Carolina, which Republicans now control but which Obama carried in 2008, "is very narrowly divided," Guillory said. Without Obama's coattails next year, he said, Hagan "needs a strong turnout from blacks, Latinos, women." They are unlikely to be moved by votes against incremental gun-control measures, he said.
Landrieu's and Hagan's decisions carry risks. They lack the political cover that would be provided if their state's other senator were a Democrat also voting for the gun background proposal.
Like them, Begich, Pryor and Heitkamp share their states with Republican senators who voted against the Obama-backed measure.
On tough votes, Democratic lawmakers must weigh the risk of inviting a liberal challenger in the next primary versus the risk of antagonizing centrist voters in a general election.
Some liberal groups are calling for primary challenges to Baucus, Begich and Pryor. The California-based "Courage Campaign" is asking Democratic donors to withhold money from groups that back those three.
Local political activists doubt such tactics will work. In Montana, for instance, Baucus is a Democratic institution, and the state party leans heavily on his legacy and fundraising.
Alaska Democratic Party spokesman Zack Fields said there has been "zero discussion" of a primary challenge to Begich.
The electoral fates of Begich, Baucus, Pryor and Heitkamp will help determine whether Democrats can thrive in largely rural states.
The latest AP-GfK poll found significantly more support for gun rights in rural states. Among rural residents, 55 percent say someone in their household owns a gun, compared with 31 percent of suburban residents and 21 percent of urban dwellers.
Wednesday's Senate vote reflected the rural nature of gun support.
The combined population of states in which both senators voted against the expanded gun background check — including Texas and Georgia — is about 78 million. The combined population of states on the losing side, in which both senators voted for the gun-control measure, was nearly double that number. That group included California, New York, Illinois, Pennsylvania, Michigan, New Jersey and Virginia.
Associated Press writers Henry J. Jackson and David Espo in Washington, Matt Gouras in Montana, Rachel D'oro in Alaska, researcher Brooke Lansdale and Director of Polling Jennifer Agiesta contributed to this report.
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