The first problem with replacing Sir Alex Ferguson was always going to be, above all else, presence. It was precisely because the legendary Scot was in charge for a barely imaginable 26 years that the choice for Manchester United should have boiled down to two men: Jose Mourinho and Pep Guardiola.
They were the only two managers who had both the utter self-assurance and extreme success to handle the inevitable fallout from such a seismic event as Ferguson retiring. It remains remarkable that, in a summer when United were "fortunate" enough that the 72-year-old departed when both of those coaches were changing jobs, they ended up with neither.
More important than anything, they were also the only two with sufficient cult of personality to make the entire narrative about them rather than just replacing the 72-year-old.
David Moyes, however, has diverted the story in an altogether different direction. It is no longer about succeeding Ferguson but saving United.
That also means that the job specification itself has changed. It is not as daunting. Were United to actually sack Moyes, it would no longer be about replacing a legend but rather an unfortunate figure who lost his way.
The club would not need someone as close in quality as possible to Ferguson, just someone better or more modern than Moyes. The current reality is this: Any more modern coach would play better football, while results can't get worse.
That, of course, means a somewhat wider potential pool of replacements. Given how dismal the current situation is, it's difficult not to think each of these prospective candidates would effect a positive change.
If he doesn't yet have the success of Mourinho or Guardiola, he certainly has the force of personality. Quite simply, Klopp is in the next tier down from those two as a manager but the likeliest of everyone else to join them. There is just something so exciting about the German.
Even aside from his whole approach, style of play and the sheer charisma, Klopp sends a ripple through the game. It might be an obvious example, but you only have to listen to the way a figure such as Zlatan Ibrahimovic talks about him. You can imagine a similar effect on United.
The Borussia Dortmund coach would just breathe life into Old Trafford again and completely change the dynamic. Beyond those kinds of intangibles, too, there is the way he is trying to push boundaries in the game: Klopp practises truly modern football.
Of course, the 46-year-old has said he does not plan to leave Dortmund until 2018 but that would also be a statement that United simply must test to the fullest. In short, since they didn't get Mourinho or Guardiola, this is the man the English champions should be striving for. It would be a new club, and a proper new era.
Louis van Gaal
The Dutch coach is almost certain at this point to go to Tottenham Hotspur, but it his own sense of certainty that should cause United to hijack that.
Van Gaal may not necessarily be the longest-term option and he may bring a briskness of his own, but that may be precisely what the English champions require at this juncture: Someone to just steady things, to restore the right kind of results and to instil a cast-iron resilience so the club can build again from a higher platform.
Van Gaal has always excelled in all of those areas. Furthermore, for all the notorious stories about how difficult he is, trophies have come rather easy to him too.
This is a man who has won a Champions League with Ajax, guided Bayern Munich to the final, won two leagues with Barcelona and then one -- most remarkably -- with AZ.
That is success across two decades, and from a broad range of challenges. In that, it is almost reminiscent of Ferguson. Van Gaal would certainly restore competitiveness.
The former England manager could represent a similar sort of choice to Van Gaal. If he is not exactly going to build a lasting dynasty, his sense of discipline would bring United closer to their natural level, and put the club back on track.
Capello is one of those managers who carries certain guarantees with regard to performance, and is not the type to be cowed by reputation or circumstance. Even if his own reputation in England isn't exactly high after his time with the national team, it should barely need to be pointed out that was basically the only "failure" of his career.
Otherwise, Capello has enjoyed success at every side he has been with: Milan, Real Madrid in two spells, Juventus and now Russia. That would indicate the problem was with England, not Capello, and that the Italian is still the kind of serious man to solve United's most immediate issues.
One of those upwardly mobile coaches in the tier behind Klopp. It could perhaps even be said Conte is where the German was around 2011, blazing through the domestic game but still just on the cusp of a proper statement on the continent.
Even if he still has some way to go in that regard, though, the Italian's winning record is significantly further along than Moyes'. His imaginative approach to tactics would also rid United of this dismally predictable rigidity.
They would be an engaging team to watch again, and there would be a sense of something modern about them again. The same would apply to a coach like Frank de Boer. Conte, essentially, would bring a retrograde team right into the realities of 2014.
Another manager who simply emanates an aura of abrasive control, and that is precisely what United need.
Put it like this, while someone such as Manuel Pellegrini is clearly an excellent coach, he is also one who really best suits specific scenarios -- the style of creative player at Manchester City, for example.
Simeone, by contrast, is the sort of bullish personality you can imagine going into pretty much any situation but having an identical effect: instilling a team with his combativeness, as well as his canniness.
United have been something of a laughing stock this season. That would simply cease under Simeone. What's more, it's not like it ends there with him. He is taking Atletico Madrid to heights that their recent history and resources should not allow. That indicates something much deeper in him, and the potential to go even further.