Critics say the administration is weakening public safety. Proponents say regulations would be where they were before President Joseph R. Biden took office. The Trump administration is scrapping more than three dozen firearms regulations, abandoning a crackdown on illegal sales, restoring gun rights to some people with mental illness and loosening oversight of private weapons transactions. The drastic retrenchment at the Bureau of Alcohol, Tobacco, Firearms and Explosives, the federal agency responsible for enforcing the nation’s gun laws, was not entirely unexpected: President Trump campaigned as a champion of gun rights. In the view of critics and even some A.T.F....