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 sounded like dystopian fiction, according to three officials familiar with the remarks, who spoke on the condition of anonymity to discuss internal deliberations: What if the White House were to withdraw the protections it provides to judges?

The U.S. Marshals Service, which by law oversees security for the judiciary, is part of the Justice Department, which Mr. Trump is directly controlling in a way that no president has since the Watergate scandal.

Judge Sullivan noted that Mr. Trump had stripped security protections from Mike Pompeo, his former secretary of state, and John Bolton, his former national security adviser. Could the federal judiciary, also a recent target of Mr. Trump’s ire, be next?

Judge Sullivan, who was nominated by President George W. Bush and then elevated to an appellate judgeship by Mr. Trump, referred questions about his closed-door remarks to the Administrative Office of the U.S. Courts, which stated its “complete confidence in those responsible for judicial security.”