WASHINGTON — The Justice Department’s top leaders listened in stunned silence this month: One of their peers, they were told, had devised a plan with President Donald J. Trump to oust Jeffrey A. Rosen as acting attorney general and wield the department’s power to force Georgia state lawmakers to overturn its presidential election results.

The unassuming lawyer who worked on the plan, Jeffrey Clark, had been devising ways to cast doubt on the election results and to bolster Mr. Trump’s continuing legal battles and the pressure on Georgia politicians. Because Mr. Rosen had refused the president’s entreaties to carry out those plans, Mr. Trump was about to decide whether to fire Mr. Rosen and replace him with Mr. Clark.

The department officials, convened on a conference call, then asked each other: What will you do if Mr. Rosen is dismissed?

The answer was unanimous. They would resign.

Their informal pact […]