The Senate agreed Thursday to move forward on gun control legislation but in addition to expanding background checks the new law would accommodate a long-standing priority of the National Rifle Association. The Post’s Karen Tumulty explains. (Christina Lee/The Washington Post)

The Senate voted 68 to 31 on Thursday to begin debating legislation to curb gun violence, launching what many expect will be weeks of deliberations on the most significant proposals to overhaul the nation’s gun laws in two decades.

As family members of the victims of a mass shooting at Sandy Hook Elementary School in Newtown, Conn., watched from the balcony, 16 Republicans joined with 52 members of the Senate Democratic coalition on a procedural motion to proceed with debate. Two Democrats joined 29 Republicans in opposing the motion.

“The hard work starts now,” Majority Leader Harry M. Reid (D-Nev.) said after the vote. Earlier, he implored his colleagues to support debating the measure: “Whichever side you are on, we ought to be able to agree to engage in a thoughtful debate about these measures.”

Debate will begin in earnest next week, when Reid said he will move to vote on a bipartisan agreement to extend the current background-check requirements to include any sale that takes place at a gun show or that is advertised in print or online.

President Obama called the Newtown families after Thursday’s vote, White House aides said. The president’s political apparatus, Organizing for Action, also sent an e-mail to supporters seeking donations and urging them to keep pressure on lawmakers.

“There is still work to be done,” said White House press secretary Jay Carney. “This was only, while important, a step in the right direction.”

Sen. Charles E. Schumer (D-N.Y.) billed the vote as a victory over the National Rifle Association, which urged lawmakers to block debate, and credited Newtown family members for helping to tip the balance.

“The only reason we are turning the page is because of you,” Schumer told Newtown families who appeared with him at a news conference. “You spoke to Congress. You spoke to the American people. We looked in your eyes, we saw your loss. We saw the hole where your child, your sibling, your parent used to be.”

Several Republicans said they will continue opposing the legislation.

Sen. John Cornyn (Tex.), the chamber’s second-ranking Republican, called the bill under consideration “a symbolic gesture” and urged Congress to focus instead on boosting federal funding for mental health programs. “We need to make sure that the mentally ill are getting the help they need, not guns,” he said.

The 16 Republicans who voted to proceed included Sens. Kelly Ayotte (N.H.), Lindsey O. Graham (S.C.) and John McCain (Ariz.), an influential trio on several policy issues. Sen. Richard Burr (R-N.C.) also voted to proceed but said he’s not a guaranteed “yes” on final passage.

“The threshold for me to vote for any gun legislation, I’m not sure could be met,” he said, adding that he’s still eager to hold a debate.

“Could I learn something that I don’t know? Possibly. Could someone come up with an angle that hadn’t been thought of? Certainly,” he said.

The two red-state Democrats who voted against proceeding, Sens. Mark Begich (Alaska) and Mark Pryor (Ark.), face difficult reelection prospects in 2014.

“We don’t need more laws restricting the Second Amendment rights of Americans, we need to better enforce those on the books,” Begich said in a statement.

Other Democrats facing difficult reelections, including Sens. Max Baucus (Mont.), Kay Hagan (N.C.) and Mary Landrieu (La.), voted to debate the measure but haven’t said whether they’ll support the overall legislative package.

The agreement on background checks — announced Wednesday by Sens. Joe Manchin III (D-W.Va.), Patrick J. Toomey (R-Pa.), Mark Kirk (R-Ill.) and Schumer — would exempt most private firearms transfers, a key concession expected to help the proposal earn bipartisan support.

The proposal also would permit gun dealers to sell firearms across state lines, and gun owners with state-issued permits to carry concealed weapons would be allowed to take their firearms through states that don’t allow concealed weapons.

Other proposed changes will come from members of both parties, including Democratic proposals to ban military-style assault rifles and limit the size of ammunition magazines; both of those are expected to fail.

Before Thursday’s vote, several senators used the personal stories of constituents to argue for or against proceeding. Sens. Chris Murphy (D-Conn.) and Richard Blumenthal (D-Conn.) used large pictures of the victims of the Newtown shooting during remarks on the Senate floor several times this week.

On the other side, Sen. Mike Lee (R-Utah) read aloud a letter from a woman he said was named Emily, a 19-year-old from Allentown, Pa.: “Gun control doesn’t solve anything, criminals will get guns no matter what. I want to protect myself as well as someone else. Please don’t take away my Second Amendment rights.”

Lee concluded: “Well said, Emily.”

Aaron Davis and Scott Wilson contributed to this report.

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