While President Biden considers a gamut of executive and legislative actions on gun control in the wake of two mass shootings, the federal agency tasked with enforcing existing gun laws remains without a permanent leader and hobbled by restrictions on its enforcement power.
The Bureau of Alcohol, Tobacco, Firearms and Explosives, or A.T.F., has long been the target of a campaign by the National Rifle Association and its legislative allies to weaken oversight of gun purchases.
“It is hard to think of any federal agency that has been so completely handcuffed as the A.T.F. has been by the N.R.A. and its friends in Congress,” said Adam Winkler, a professor of constitutional law specializing in gun statutes at the University of California, Los Angeles.
Mr. Biden, who made an emotional appeal on Tuesday for Congress to enact gun control legislation, has not yet picked a nominee to lead the agency.
White House officials said they had no timetable for doing so, but two administration officials with knowledge of the situation said that several potential candidates were being interviewed — although no names have yet been floated on Capitol Hill or among advocacy groups, according to the officials.
“The administration is going to revitalize A.T.F. and ensure that our guns laws are vigorously enforced,” said Michael Gwin, a Biden spokesman.
Still, the delay in naming a director is emblematic of the enormous practical and political challenges that come with efforts to make any significant changes at the agency.
Over the last two decades, Republicans, with the support of conservative Democrats, have embedded into spending bills riders intended to constrain the bureau, including limits on unannounced inspections of gun dealers, prohibitions on documenting the inventories of gun shops and an especially damaging provision that bars the agency from digitizing its records.
Gun rights groups say such steps are necessary to keep the A.T.F. from mounting an “assault” on the rights of gun owners. But critics consider it part of an effort to shield gun companies and owners from oversight and responsibility.
“What’s been done to the A.T.F. is systemic, it’s intentional, and it’s a huge problem,” said T. Christian Heyne of Brady: United Against Gun Violence, a gun-control group that has proposed a plan for executive action on the issue centered on stepped-up enforcement by the agency.
Mr. Biden is expected to roll out a series of executive orders related to gun violence in the coming weeks. Almost all of the orders require a significant expansion of A.T.F. enforcement. But even naming someone to lead the agency is a headache.
In 2006, N.R.A.-allied lawmakers enacted a provision making the position of A.T.F. director, which had previously been a political appointment, subject to Senate confirmation.
As a result, only one director has been confirmed over the last 15 years: the Obama nominee B. Todd Jones. Regina Lombardo, a well-regarded agency veteran who helped direct the federal response to the Pulse nightclub massacre in Orlando in 2016, has served as acting director since early 2019.
She got the job after former President Donald J. Trump, who ran on a defiantly pro-gun platform, withdrew the nomination of a former top police union official, Chuck Canterbury, after the nominee refused to entirely rule out expanding background checks and other safeguards.
The agency’s potential power was another reason Mr. Canterbury failed. One of Mr. Trump’s closest allies, Senator Josh Hawley of Missouri, opposed him, warning that Mr. Canterbury might use the bureau’s authority to more strictly enforce gun laws.
