On March 11, about 50 judges gathered in Washington for the biannual meeting of the Judicial Conference, which oversees the administration of the federal courts. It was the first time the conference met since President Trump retook the White House.In the midst of discussions of staffing levels and long-range planning, the judges’ conversations were focused, to an unusual degree, on rising threats against judges and their security, said several people who attended the gathering.Behind closed doors at one session, Judge Richard J. Sullivan, the chairman of the conference’s Committee on Judicial Security, raised a scenario that weeks before would have...