In August 2017, Mr. Sessions, as the attorney general, condemned the “dramatic growth in the number of unauthorized disclosures of classified national security information in the past several months.”
Under the Obama administration, the Justice Department also aggressively pursued officials who provided reporters with delicate information. In 2013, prosecutors obtained the phone records of reporters and editors of The Associated Press. In that instance, law enforcement officials obtained the records for more than 20 telephone lines of its offices and journalists, including their home and cellphone numbers.
In addition, the Justice Department seized the phone records of James Rosen, then a Fox News reporter, after one of his articles had included details of a secret United States report on North Korea. An affidavit described Mr. Rosen as “at the very least, either as an aider, abettor and/or co-conspirator.”
The Justice Department’s decision to seek the phone records was widely condemned in the news media.
In 2013, the attorney general at the time, Eric H. Holder Jr., issued new guidelines that significantly narrowed the circumstances under which journalists’ records could be obtained but did not preclude prosecutors from seeking phone records and emails for national security reasons.
In a July 2017 email, Sarah Isgur Flores, then a top spokeswoman for the Justice Department, tried to cast doubt that a meeting had happened at all between Mr. Kislyak and Mr. Sessions. She described the intercept as “debunked” and questioned its credibility as she defended Mr. Sessions in the news media.
Ms. Isgur described the news reporting as “serious leaks to our national security.” The email was obtained by the reporter Jason Leopold of BuzzFeed News under the Freedom of Information Act.
Last year, the Trump administration declassified sensitive transcripts of Mr. Kislyak speaking with Mr. Trump’s former national security adviser Michael T. Flynn. The documents also revealed highly delicate F.B.I. abilities, showing that the bureau was able to monitor the phone line of the Russian Embassy in Washington even before a call from Mr. Kislyak connected with Mr. Flynn’s voice mail.