Last week's surprise forced resignation of Jeff Sessions as attorney general of the United States set in motion a series of events that will soon resonate in all corners of the Department of Justice.

President Donald Trump has been steamed at Sessions ever since Sessions removed himself from supervision over the DOJ's investigation into whether a conspiracy existed between Russian agents and the Trump campaign in 2016 for the Russians to provide assistance to the campaign — a felony.

Sessions' recusal was perfectly rational and ethically required; he had been a high-ranking official in the campaign and would probably be interviewed as a witness in the investigation. Because ethics rules prohibit DOJ officials from being witnesses in cases that they supervise, Sessions passed the case to his deputy, Rod Rosenstein, who promptly appointed former FBI Director Robert Mueller as special counsel to head the investigation.

When the special counsel began flexing his prosecutorial muscles a little too close to Trump Tower and the Oval Office for Trump's comfort, Trump's blood pressure rose, and he asked Sessions to sign and deliver an undated letter of resignation, which Sessions did. On Nov. 7, the day after the midterm elections delivered the House of Representatives comfortably to the Democrats, Trump released the still-undated letter, and Sessions was out of a job.

Then Trump began another legal firestorm by naming Sessions' chief of staff, Matthew Whitaker, acting attorney general. He did this even though the federal statutes governing succession in the DOJ state that upon a vacancy in the office of attorney general, the deputy attorney general — in this case, the same Rod Rosenstein — shall become the acting attorney general.

In bypassing Rosenstein for Whitaker, Trump has added to the woes he will face when the Democrats take control of the House in early January. That's because of lingering and now public doubts about Whitaker's professional qualifications for office and clear statutory language that makes him legally ineligible to be acting attorney general.

Here is the back story.

Every federal executive department, from Defense to Treasury to Justice, has a principal officer — usually called the secretary but called the attorney general for Justice — and a deputy. Neither position can be occupied without a presidential appointment and a Senate confirmation.

The main purpose of the deputy is to be ready to fill in for the principal when that office becomes vacant. Congress created the office of deputy attorney general for the express purpose of having a presidentially appointed and Senate-confirmed person in the wings should the attorney general's office fall vacant. On Nov. 7, the office fell vacant.

Should the president wish to bypass the deputy attorney general, he may do so, but he may only designate a person who already occupies a DOJ position that is presidentially appointed and Senate-confirmed. Whitaker, Sessions' former chief of staff, was not in a presidentially appointed or Senate-confirmed job at the time Trump named him acting attorney general.

Whoever runs the DOJ has such vast power over its 90,000 employees, including the FBI — not to mention that he or she is seventh in the presidential line of succession and has the unchecked power to commence criminal investigations, seek and obtain indictments, and terminate criminal investigations already begun — that Congress passed statutes to ensure that no one could hold that job who has not been scrutinized by the rigors of Senate confirmation.