Rudy Giuliani's assertion to CNN this week that President Donald Trump can't be indicted by the special counsel , and thus can't face a subpoena, banks on a series of internal Justice Department policies.
The question to this day is untested in the court system. Yet the step-by-step process Robert Mueller or any special counsel could follow for a President under investigation has several possible outcomes.
According to several legal experts, historical memos and court filings, this is how the Justice Department's decision-making on whether to indict a sitting president could play out:
First, there must be suspicion or allegations of a crime. Did the President do something criminally wrong? If the answer is no, there would be no investigation.
But if the answer is maybe, that puts federal investigators on the pursuit. If they find nothing, Justice Department guidelines say they'd still need to address their investigation in a report summarizing their findings.
If there could be some meat to the allegations, the Justice Department would need to determine one of two things: Did the potentially criminal actions take place unrelated to or before to the presidency? Or was the President's executive branch power was crucial in the crime?
That determination will come into play later, because Congress' power to impeach and remove a president from office was intended by the framers of the Constitution to remedy abuse of the office, legal scholars say.
Perhaps, though, the special counsel decides there's enough evidence to prove that the President broke the law.
That's where the Office of Legal Counsel opinions come in.
In 1973 and 2000, the office, which defines Justice Department internal procedure, said an indictment of a sitting president would be too disruptive to the country. This opinion appears to be binding on the Justice Department's decision-making, though it's possible for Deputy Attorney General Rod Rosenstein to choose to override the opinion, give Mueller permission to ignore it and take it to court, or ask the office to reexamine the issue by writing a new opinion.
This sort of legal briefing has been done before, like in the year after the 1973 opinion, when then-special prosecutor Leon Jaworski wrote a Watergate-era memo describing why the President should not be above the law.
Of course, there's another immediate option if a special counsel finds the President did wrong. Prosecutors could use the "unindicted co-conspirator" approach. This would involve the special counsel's office indicting a group of conspirators, making clear the President was part of the conspiracy without bringing charges against him.
At any time, in theory, a special counsel could decide to delay an indictment until the President leaves office -- so as not to interfere with the functioning of the executive branch. The other options would be to drop the case or send an impeachment referral to Congress. As evidenced by Mueller's actions previously in the investigations of Trump's personal attorney Michael Cohen and former campaign chairman Paul Manafort, any steps this special counsel takes will likely come with the full support of the acting attorney general on the matter, Rosenstein.
The question of whether a President could be subpoenaed is a story for another day.