WASHINGTON — President Trump attacked Attorney General Jeff Sessions yet again on Wednesday [July 26, 2017] extending a campaign against Mr. Sessions with what has become near-daily insults and criticism, both in private and in public.

Mr. Trump has made clear that his frustration with Mr. Sessions, the former Alabama senator who was one of his earliest campaign supporters, stems from the attorney general's decision to recuse himself from the investigation into Russia's interference in the 2016 election and whether Mr. Trump's associates conspired with Russia.

The pattern has fueled suspicion that Mr. Trump is trying to bully Mr. Sessions into resigning — and might fire him if he does not leave voluntarily — in order to clear the way for a replacement who would take control of that investigation. Here is a breakdown of possible legal and procedural paths such a maneuver could take.

Why is it harder to fire Mueller with Sessions in place?

While most executive branch officials can be fired at will, the special counsel leading the Trump-Russia investigation, Robert S. Mueller III, is protected by Justice Department regulations. They say he can be "removed from office only by the personal action of the attorney general" and only for "good cause," such as misconduct.

Because Mr. Sessions is recused, his deputy, Rod J. Rosenstein, is the acting attorney general for that inquiry. He appointed and oversees Mr. Mueller. While Mr. Trump also nominated Mr. Rosenstein, a former United States attorney, he has vowed to "defend the integrity" of the investigation, including by refusing to fire Mr. Mueller without good cause.

If Mr. Trump were to order Mr. Mueller fired and Mr. Rosenstein refused — and then resigned or was himself fired by Mr. Trump — it could set up a repetition of the so-called Saturday Night Massacre of 1973, in which Richard M. Nixon's search for a Justice Department official willing to fire the special counsel investigating the Watergate scandal prompted a cascade of resignations. That would increase political risks for Mr. Trump.

What could a new attorney general do?

A new attorney general who is not recused from the Trump-Russia investigation would take over from Mr. Rosenstein as the overseer of the special counsel investigation and could fire Mr. Mueller — either by declaring that Mr. Mueller has overstepped in some way, or by first modifying Justice Department regulations to eliminate the rule protecting special counsels.

A new attorney general could also declare that the regular Justice Department can handle the investigation after all, disbanding Mr. Mueller's staff. And he or she could direct investigators to swiftly wrap up their work while narrowly interpreting their jurisdiction, such as limiting their ability to scrutinize whether Mr. Trump's interactions with James B. Comey, the former F.B.I. director fired by the president, amounted to obstruction of justice.

How much latitude would Mr. Trump have to pick a new attorney general?

If the attorney general's office becomes vacant and Mr. Trump merely nominates someone else to fill it, Mr. Rosenstein would serve as the acting attorney general for the time being until the Senate confirmed that pick, according to a statute. Mr. Trump could also appoint a different acting attorney general under the Vacancies Reform Act, but it limits his options to senior Justice Department officials who have been in their positions at least three months, or other Senate-confirmed government officials.

If Mr. Trump wants to unilaterally install anyone else as attorney general without going through Senate confirmation, he might be able to do so under the Constitution's recess appointment clause. It empowers presidents to fill vacant positions during Senate recesses in excess of 10 days. A recess-appointed attorney general would stay in power until January 2019, when the next Congress is seated.

Will the Senate's August recess present an opportunity?

It could. If the chamber goes into a formal recess before leaving Washington next month for its annual break, Mr. Trump could make recess appointments while senators are on vacation.

Can the Senate block Trump's recess appointments?

Yes. Congress can prevent presidents from making appointments during its breaks by holding so-called pro forma sessions, in which a senator comes into the otherwise-empty chamber every few days and bangs the gavel. That technically breaks up a long recess into a series of short ones — each too brief to trigger appointment powers.

Could Democrats alone block Trump?

That is not clear. The Senate minority leader, Chuck Schumer, Democrat of New York, called upon Republicans on Tuesday to use pro forma sessions in August to prevent Mr. Trump from appointing "someone during the August recess who will fire Special Counsel Mueller and shut down the Russia investigation." He also vowed that Democrats would try to do that on their own if Republicans refused.

Before the Senate adjourns for more than three days, Congress adopts a concurrent resolution giving it the authority to do so. That is normally routine, but Democrats are discussing whether to try to block any up-or-down vote on such a resolution by offering an unlimited series of amendments to its date and time for reconvening. If the Senate gives up and leaves town without such a resolution, the Constitution would require pro forma sessions every three days, blocking recess appointments.

Could Republicans overcome such a move?

Alan S. Frumin, who served as the Senate's chief parliamentarian from 1987 to 1995 and from 2001 to 2012, said Republicans could "quash such a filibuster by amendment" using what some call the nuclear option to change the rules. Under that scenario, if a majority of senators vote to deem the Democrats' amendments "dilatory," they could adjourn in a way that leaves Mr. Trump free to make recess appointments. But if at least three Republican senators break ranks, the Senate would need to meet every three days.

The Constitution also says that if the House and Senate disagree when to adjourn, the president "may adjourn them to such time as he shall think proper." That suggests Mr. Trump might be able to force the Senate into a lengthy recess. But no president has tried to exercise this power, and it is not clear what would constitute such a disagreement: Mr. Frumin said that the House typically gives its consent for the Senate to adjourn for more than three days but does not order the Senate to do so.

"This would be an enormous political and constitutional danger," he said. "If he can force them into adjournment, he can in essence terminate Congress."

What would be the political fallout?

Firing Mr. Sessions and Mr. Mueller would be a shocking moment for Washington, where many Republicans in Congress have expressed support for Mr. Mueller and conservatives like Mr. Sessions. But Republicans have also shown no appetite for impeachment proceedings to replace Mr. Trump with Vice President Pence, and it is an open question what, if anything, it would take to change that.

On Tuesday, House Speaker Paul D. Ryan, Republican of Wisconsin, was asked about Mr. Trump apparently laying the groundwork to fire Mr. Sessions and make a recess appointment of someone who could fire Mr. Mueller. He was asked if he was concerned.

"Look, the president gets to decide what his personnel is," Mr. Ryan replied, adding: "He determines who gets hired and fired in the executive branch. That's his prerogative."

This encyclopedic article on what could happen is by Charlie Savage and appeared on the New York Times on July 26, 2017.

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July 31, 2017