"Mr. Sessions submitted his resignation, touching off a scramble among White House aides to keep the president from accepting it. While he let Mr. Sessions keep his job, Mr. Trump pocketed his resignation letter and set off fears within the White House that he would wield it to get what he wanted from law enforcement officials.
Reince Priebus, the former White House chief of staff, told Mr. Sessions that the president could use the letter as a kind of “shock collar,” according to the report, and he told Mr. Trump that he had “D.O.J. by the throat.” It took Mr. Priebus two weeks to get the president to hand over the letter."
https://www.nytimes.com/2019/04/19/u...k-mueller.html