WASHINGTON — B. Todd Jones became the first Senate-confirmed director of the ATF on Wednesday, but only after a fierce lobbying effort swayed a single Republican to change what proved to be the pivotal vote.

Democrats had expected a close result, but were confident they had the votes to end a Republican filibuster of Jones’ nomination to lead the Bureau of Alcohol, Tobacco, Firearms and Explosives when they decided to bring it to the Senate floor this week.

But a dramatic scene began to play out when Sen. Lisa Murkowski of Alaska, one of the Republicans that Democrats had expected to break from the minority party, cast an initial “no” vote on whether to end a filibuster. After five other Republicans voted “yes” and it was clear Murkowski’s would be the decisive vote, the Alaska senator was surrounded in the well of the chamber by senators from both parties, including members of the leadership and the top Democrat and Republican on the Judiciary Committee, who could be seen pleading their cases.

At one point, Sen. Susan Collins of Maine, one of the Republicans who had voted to advance Jones’ nomination, pulled Murkowski off the Senate floor to talk in private.

“I was concerned that she was being pummeled by both sides, and thought she might need a little break,” Collins later told reporters, joking that they just chatted about a recent dinner Murkowski had hosted at her home.

After nearly an hour, Murkowski returned to the Senate floor and announced she would instead vote “yes” to allow a confirmation vote.

At first she ignored questions from reporters as she hurried to her office for a meeting with the director of the Indian Health Service. But in an interview later, Murkowski said that she had understood there was an ongoing investigation into Jones’ handling of whistleblower complaints when he served as U.S. attorney in Minnesota, and that she had seen that as an appropriate justification for blocking his nomination.

That investigation had been the focus of Republican concerns with Jones’ nomination. Iowa Sen. Charles E. Grassley, the top Republican on the Judiciary Committee, said confirming him under such circumstances would send “a chilling message to all employees” of the ATF.

But other colleagues told Murkowski the investigative phase had concluded and mediation had begun.

“I think it was an important conversation to have with my colleagues on the Judiciary Committee, those that have been involved with the vetting,” she said. “That changed the direction for me.”

Murkowski later voted against Jones, but he was confirmed by a 53-42 vote.

President Barack Obama nominated Jones to be the permanent director in January, as he rolled out a series of other executive actions to address gun violence in response to the school massacre in Newtown, Conn. Jones had been the agency’s acting director since 2011, when the previous director was dismissed amid fallout from Operation Fast and Furious, the failed gun-tracking operation.

His status remained in doubt for much of the year as Republicans moved to block his nomination and a number of others. The National Rifle Association has also typically mounted opposition to the confirmation of ATF leadership.

But the NRA’s late decision to remain neutral on Jones’ confirmation, and a separate agreement between Senate Democrats and Republicans to process other stalled nominations, led Democrats to believe they could round up the needed 60 votes to break a GOP filibuster.

Murkowski, in fact, had been key to that agreement. She was one of just six Republicans to vote to allow confirmation votes to proceed on Thomas E. Perez, Obama’s nominee for labor secretary. And just Tuesday, she was the only Republican to vote in favor of the president’s two new nominees for the National Labor Relations Board.

Murkowski has in recent years become a key swing vote, often breaking with Republicans to support Democratic initiatives. First appointed to the Senate in 2002 after her father resigned his seat to become governor, Murkowski won a second full term in 2010 after first losing in a Republican primary to a tea party-backed challenger. She waged a successful write-in campaign to win in the general election.

At one point, as senators on both sides jockeyed for Murkowski’s attention, Senate Majority Leader Harry Reid, D-Nev., pulled Sen. John McCain, R-Ariz., into the scrum to help lobby his fellow Republican. McCain had helped broker the agreement that ended a showdown between the parties over threatened rules changes on nominations.

Other senators later said concern about a return to the brinkmanship over filibuster rules was part of the case made to Murkowski.

“We’ve been able to march through some really difficult nominations like NLRB and EPA, and the last thing we want right now as we head into the fall, where I still think there is a good chance we could get some kind of bipartisan agreement on the budget and on the debt … is to leave with some radioactive blowup,” said Sen. Amy Klobuchar, D-Minn., a lead supporter of Jones’ nomination.

Another major factor, Klobuchar said, was the fact that since a 2006 law passed that required Senate approval of ATF directors, no nominee had been confirmed.

“At some point, why would you have a confirmable position when under both George Bush and Barack Obama the Senate has refused to confirm anyone?” she said.

David Chipman, an ATF agent for 25 years who now works with the group Mayors Against Illegal Guns, said installing Jones as full-time director was a significant step in efforts to prevent gun violence. Chipman called him “the kind of leader that can make a difference.”

“But let’s be clear: He needs the resources to make a difference,” Chipman added, noting that the agency is smaller than the Broward County, Fla., sheriff’s office. He said Jones will be confronted with an agency in which half of the workforce can retire over the next three years.

“How is he going to stabilize the infrastructure to make ATF viable in a tight budget environment?” Chipman asked. “Their budget is just over a billion dollars. There are weapons systems that cost hundreds of billions of dollars.”

Distributed by MCT Information Services