(Reuters) - Ah the legal hypothetical — a time-honored favorite of law professors and judges to force advocates into defending absurd positions.

There were some doozies on Tuesday when the U.S. Court of Appeals for the D.C. Circuit sitting en banc took up the Michael Flynn case. Over a nearly four-hour hearing, the 10 judges considered whether to compel the trial court judge to grant a motion to dismiss the criminal case against Flynn, who briefly served as President Donald Trump's national security advisor.

For such a sexy, high-profile case, the actual legal decision may turn on a fairly narrow question: At what point in judicial proceedings is granting a writ of mandamus appropriate?

But the judges' hypothetical questions, which included imagining a U.S. attorney and the attorney general together accepting a suitcase full of cash from opposing counsel, may help the members of the court contemplate the far bounds of their decision.

Plus it's more fun than only talking about mandamus.

Flynn, you may recall, pleaded guilty to making false statements to federal investigators in late 2017 but asked to withdraw the plea in January 2020 after hiring new counsel.

In May, the Justice Department abruptly filed a Rule 48 motion to dismiss the case against Flynn, claiming that based on newly-discovered evidence showing misconduct by the FBI, it could no longer prove beyond a reasonable doubt that any false statements Flynn made were material to the investigation.

But U.S. District Judge Emmet Sullivan wasn't ready to rubber stamp the government's request. Instead, he appointed Debevoise & Plimpton partner John Gleeson, a former federal judge, as amicus.

Sullivan called on Gleeson to present arguments in opposition to the government's motion to dismiss, with a hearing scheduled for July 16.

That's when Flynn's legal team led by Sidney Powell of Sidney Powell P.C. petitioned the D.C. Circuit for a writ of mandamus. Powell asked the appeals court to find Sullivan exceeded his authority by refusing to dismiss Flynn's case immediately and appointing an amicus instead. In June, Powell prevailed before a split three-judge panel before the full court agreed to hear the matter en banc.

There's a reason why mandamus is known as an extraordinary writ. It's only supposed to be issued in exceptional circumstances, when a petitioner has no other adequate means to obtain relief.

But here, Sullivan had yet to rule on the motion to dismiss—all he'd done was ask for briefing.

The first question of the en banc hearing got right to the point. Chief Judge Sri Srinivasan asked Powell if she agreed that her client was only entitled to mandamus "if there is no other means to obtain the relief?"

"Yes, your honor," she replied, adding that there was no other relief available because the district court had usurped the power of the executive branch.

"Are you aware of any other case in which mandamus has been granted to compel a district court to decide a pending motion in a particular way, either by granting or denying it, before the district court itself has decided to grant or deny the motion?"

Powell eventually admitted she was not aware of other such cases, but she said that was only because no other court had done what Sullivan did in Flynn's case.

Srinivasan pressed further, "If the district court had granted the motion, then that would be adequate alternate means, would it not?"

Based on subsequent questions from the other judges, it seems possible this could be the dispositive point — that the en banc court will find it was premature to grant a mandamus petition before Sullivan had a chance to rule on the motion to dismiss. After all, if Sullivan had granted the motion and closed the case, what would there be left to complain about?

As Wilkinson Walsh name partner Beth Wilkinson, who represented Sullivan, put it, "This matter could have been over on July 16, ironically, if the judge could have had his hearing."

But the en banc court went further to consider extreme scenarios, probing how much leeway a judge has to reject a Rule 48 motion to dismiss, for example.

Judge Patricia Millett had one of the most compelling hypotheticals. To acting Solicitor General Jeffrey Wall, she posed this scenario — imagine a criminal case, where the judge asked the government repeatedly if all potentially exculpatory materials had been turned over, and was told yes.

"Now the first day of trial, in the presence of the court, the defendant's attorney hands to the prosecutor a briefcase, filled to overflowing with 20 dollar bills falling out of the seams," Millett said. "It's handed to the prosecutor, with the U.S. attorney and the attorney general sitting there next to her."

Upon receipt of the briefcase, she continued, what if the government then submitted a Rule 48 motion to dismiss, now claiming that potentially exculpatory materials had not been turned over?

Is it Wall's position that the judge, who has just witnessed an outright bribe, would still have to grant the government's motion to dismiss?

Yes, Wall said, adding that the court could still impose sanctions.

Millett took an equal opportunity approach to her hypotheticals, asking Wilkinson to imagine a situation where a person is in jail awaiting trial when the government finds exculpatory DNA evidence and files a Rule 48 motion to dismiss the case.

What if the judge, like Sullivan, took weeks to decide the request? Shouldn't that prisoner be allowed to seek immediate mandamus relief, Millett asked.

Wilkinson hedged, noting that Flynn is not incarcerated, nor had he requested expedited briefing — and that unlike a prisoner, he is not facing the kind irreparable harm that would justify mandamus.

If the mandamus decision in Flynn's case stands, she added, "it would open the floodgates to other people not happy with district courts."