President Trump, who owns a handgun and has a New York State permit to carry it hidden, has killed a rule that President Obama put in place before leaving office that would have limited access to guns by some of the more than 70,000 mentally ill who receive full disability benefits from the Social Security Administration. The Obama measure was opposed by both the National Rifle Association and the American Civil Liberties Union, an apparent anomaly that points to the possibility, however far-fetched, that strict gun control could become a nonpartisan effort, as it should.