One would think that falling under the Treasury Department, job one would be ensuring the collection of taxes.
The ATF or BATFE is no longer part of the Treasury Department, and they no longer deal with the taxation of alcohol or tobacco.
As of 2002 that is done by the TTB or Alcohol and Tobacco Tax and Trade Bureau.
The ATF/BATFE was transfered from the Treasury Department to the Justice Department under the Homeland Security Act of 2002 starting in 2003.
They are now solely a LEO branch, not a treasury Bureau.
The A and the T of BATFE are just kept to keep from calling them the "Firearms and Explosives Bureau".
Thier almost sole role now is the enforcement of gun control, lending occasional assistance on explosives related cases, but even those are primarily dealt with by the FBI.
So they would be better called the Firearms Bureau.
I imagine that would sound too anti-gun though. So they keep the name long and meaningless. Toss in something about Tobacco and Alcohol for good measure. Throw in "Explosives". An viola you don't sound like a purely anti 2nd Amendment agency.
They do assist in explosives and arson cases, but the FBI is the workhorse on those.
They mainly deal with gun control. Anything related to guns or gun control or the application of gun laws.