WASHINGTON — For years, the Bureau of Alcohol, Tobacco, Firearms and Explosives has been overlooked in Washington. Overshadowed by more politically powerful law enforcement agencies like the F.B.I., the A.T.F. garnered headlines mostly for notorious episodes, including the deadly 1993 siege in Waco, Tex., and the “Fast and Furious” gunwalking scandal more than a decade later.

Now, the A.T.F. is on the verge of a crisis. The agency, which has not grown significantly since its founding in 1973, is about to confront a staffing shortage and is set to lose its tobacco and alcohol enforcement authorities. President Trump has yet to nominate a director to oversee the agency, which has been without permanent leadership for eight of the past 12 years.

Amid the dearth of leadership and resources, the White House is pushing the A.T.F. to the forefront of its fight against violent crime. In response to the mass shooting at a Florida high school last week, Mr. Trump, who promised to fight violent criminal gangs and illegal guns — two of the A.T.F.’s key missions — announced that he would be relying on the bureau to regulate so-called bump stock accessories.

But it is all but politically impossible for Mr. Trump, who counts the powerful gun lobby among his most ardent supporters, to strengthen the A.T.F. The National Rifle Association has long sought to hobble the agency in an effort to curb its ability to regulate guns, which the gun lobby has traditionally opposed.