The confirmation of US Attorney Michael J. Sullivan as head of the Bureau of Alcohol, Tobacco, Firearms, and Explosives was thrown into further doubt yesterday, when a Republican senator who is blocking the nomination renewed complaints that Sullivan has refused to loosen licensing rules for guns. The development means that the future leadership of the US attorney's office in Boston will remain cloudy for the foreseeable future, because the Bush administration has been unable to nominate a replacement. For now, Sullivan is performing both roles while his nomination is caught in a crossfire over gun policy. Senator David Vitter of...