Fired FBI Director James Comey has emerged as the main figure in what some Democrats believe will be an obstruction of justice case against President Trump in the Trump-Russia matter. Comey's stories of conversations with the president, plus the fact that he was fired, ostensibly as a result of the Russia probe, make him potentially the star witness in the case.

Which brings up an intriguing legal question. Comey is a good friend of special counsel Robert Mueller — such a good friend, for about 15 years now, that the two men have been described as "brothers in arms." Their work together during the controversies over Bush-era terrorist surveillance has been characterized as "deepening a friendship forged in the crucible of the highest levels of the national security apparatus after the 9/11 attacks," after which the men became "close partners and close allies throughout the years ahead."

Now Mueller is investigating the Trump-Russia affair, in which, if the increasing buzz in the case is correct, allegations of obstruction against the president will be central. And central to those allegations — the key witness — will be the prosecutor's good friend, the now-aggrieved former FBI director.

Is that a conflict? Should a prosecutor pursue a case in which the star witness is a close friend? And when the friend is not only a witness but also arguably a victim — of firing — by the target of the investigation? And when the prosecutor might also be called on to investigate some of his friend's actions? The case would be difficult enough even without the complicating friendship.

This is by no means a definitive answer, but I put that question to five Washington lawyers Sunday — lawyers in private practice, on Capitol Hill, in think tanks, some of them veterans of the Justice Department. The verdict came back mixed. But the answers made clear this is a question that will have to be answered in the course of the Mueller investigation.

"This is very odd," said one big-firm lawyer and Justice Department veteran Sunday:

An ordinary prosecutor would turn this over to someone uninvolved, and there would be lots of candidates. That is particularly so here where Comey is not just the star witness but a potential target. That said, I doubt anyone outside can or should do anything here. Mueller should resign, but if he chooses not to — either on the theory he can handle the conflict, or on the theory it is such a mess he should just persevere — the attorney general should not fire him. As to how Mueller might handle, he could announce that the Comey part of the case will be handled by someone else within his office, but that is complex and not very satisfactory.

On the other hand, from another big-firm lawyer and Justice Department veteran:

I don't see any problem with a prosecutor being a friend of a potential witness. It's hard to imagine a scenario, for example, where information acquired as part of a friendship would impair the prosecutor's ability to do his or her job or, alternatively, improperly influence the witness' testimony. I expect, in any event, that any interview of Comey would be very much a group effort on the part of Mueller's team, so that his personal relationship with Comey would hardly be an issue.

From a Capitol Hill veteran now in private practice:

They [Comey and Mueller] have a mutual admiration society. Mueller should hire another prosecutor to deal with Comey. But Comey is central to their case, so it infects the whole prosecution. Could [a close colleague] investigate me? No, he would recuse. But Mueller's stature is great, and he may be able to overcome it.

From another Justice Department veteran:

I think it raises a serious conflict of interest that would normally require the prosecutor to recuse himself from the case.

And finally, from another Hill lawyer:

It's somewhat ironic, no? I mean, the whole purpose of the special counsel is to have a prosecutor from outside the government and outside of the normal chain of command because inherent conflicts render the Justice Department incapable of handling it. So, now the special counsel is a close friend (mentor/mentee relationship) with the star witness, who by his own admission leaked the memos at least in part to engineer the appointment of a special counsel. Only in Washington. You can't make this stuff up.