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When Jose Mourinho took over at Manchester United in May 2016, he did so on a tidal wave of optimism.

The story of the post-Sir Alex Ferguson years does not need repeating here, but a winner, a man whose players will run through brick walls for him and someone who had always seemed to have a glint in his eye around Old Trafford seemed the perfect person to right the giant listing ship.

And so far, for the most part, so good. He has won two major trophies and the Community Shield, got the team back into the UEFA Champions League and all but mathematically won their qualifying group in four games. A United side that had finished seventh, fourth and fifth in the three seasons that preceded his arrival are second in the Premier League table.

A sixth-placed finish last season was disappointing, but the UEFA Europa League trophy more than made up for it.

However, the wobble that has followed in the wake of the 0-0 draw at Anfield on October 14 has seen a surly Mourinho oversee defeats at Huddersfield and Chelsea as Manchester City have opened up a big gap at the top of the table.

Worse than that have been the stories—including one written by Duncan Castles, a man with good contacts in Mourinho's camp, for the Daily Record—that the manager could leave United over frustrations about the way the club does business.

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Now, were he to do so, it could be argued he was deflecting attention from his own inability to compete with Manchester City under Pep Guardiola, but that is all speculative.

What is not speculative is that he will leave at some point, and history tells us it will not be that long before he does. While United fans fed up with the instability of recent years might hope rumours he is considering leaving this season are false, it is hard to hope he will stay much beyond the end of next season. Three and out is Jose's usual business model.

If history repeats, we are just about halfway through his likely tenure, and in order to get the succession planning right, it is sadly time to start thinking about it already. We asked United fans on Twitter which person they saw as the sensible heir to Mourinho's throne.

The results can be divided into four categories. The first was those people bemoaning the fact the question was being asked. There was something of a presumption that asking who should be next boss was advocating Mourinho's removal, which would be a faintly ridiculous position to hold at this point.

It was not championing for anything—rather it was asking the question about who should take over when he does leave, be that sooner or later.

The second category was joke answers. This is inevitable on Twitter, and there were plenty of good ones, with West Ham United's newly appointed manager getting a mention or two:

Someone threw their hat into the ring, assuming their latest Football Manager save goes well. People lobbied for cloning technology to be put to work on Sir Alex Ferguson. There was, in general, a lot of banter:

While much of this was funny, it was easy to wonder whether part of the reason for the instinct to joke about it is that it is quite a difficult question to answer.

The third group contained those who suggested an assortment of managers doing good work:

Diego Simeone would seem an odd choice given his style of football. He has had phenomenal success at Atletico Madrid in the face of a duopoly that makes his achievements all the more remarkable. But a defence-first 4-4-2 would probably not go down well with the United faithful after the (justified) criticism Louis van Gaal received over his style of play and that Mourinho has received about his approach to big games.

Leonardo Jardim would represent a huge risk, though the job he has done at AS Monaco has been outstanding. The crowd-pleasing, Ligue 1-winning side he managed last season lost many vital components in summer 2017, particularly with the loan move of Kylian Mbappe to Paris Saint-Germain—a move that must surely have stuck in the manager's craw—but he has kept pace with PSG in the league.

Monaco are just four points off the side that took Mbappe from them and added Neymar to their already formidable attack. They are struggling a bit in the Champions League, but reaching last season's semi-final was still a seminal achievement. His lack of history at managing the game's biggest clubs would make his appointment a big risk.

Thomas Tuchel has a big reputation, but in truth it remains untested at the highest level. His interview would have to be very convincing.

Carlo Ancelotti has the qualification but would continue the cycle of short-term mega-coaches.

Back in September 2015, I wrote that Ryan Giggs should be given the job. It was obviously naive at the time and looks even more so now. In my defence, the logic was he would succeed directly from a successful Van Gaal in orderly fashion, with a squad he knew in a system that suited the players at his disposal. It would have been a gamble then. Now it would be the gamble to end all gambles.

The fourth, and by a good margin the largest, group comprised those who suggested the Premier League's most up-and-coming manager. In fairness, Mauricio Pochettino has probably crossed the line from up-and-coming to arrived, having taken Tottenham Hotspur to third- and second-placed finishes in the past couple of seasons.

From a distance, Pochettino's most impressive achievement has been the consistent improvements he has made to the players at his disposal. The most frustrating thing about being a United fan in the post-Fergie era has been the sense the team is less than the sum of its parts, that good players are playing averagely well and average players are playing badly. Under Sir Alex, United had rough patches but could pretty much always be relied upon to play to the best of themselves.

Pochettino has done that with Spurs. Take a player like Christian Eriksen, who was considered a good prospect in his Ajax days but someone whom no truly elite club was prepared to gamble. Under his Argentinian manager's instructions, he has become one of the Premier League's most impressive No. 10s. Across defence, midfield and attack, almost the entire squad has thrived.

There are two major question marks over Pochettino's suitability. One is he has not won major silverware. That is a significant knock against him, but considering the circumstances of 21st-century Premier League football, it is hard to hold it too heavily against his achievements.

The domestic cup competitions are a distraction from the key priorities against which his job performance is judged. He could perhaps have done more when Leicester City won the league in 2015/16, but that was an incredibly strange season. And had any other team won the title, no one would hold Spurs' finish against Pochettino.

The second, and probably more pertinent, question that hangs over him is this: Would he come? While history tells us United are a much bigger club that Spurs, the balance of power is shifting. They are constructing a massive new stadium that will change the profile of the club significantly.

Tottenham's youth setup is superb, and Pochettino has a chance to build something special. Everyone has been assuming for a while that his team would eventually be picked apart, but that has not happened yet. And at Spurs, he has tremendous capital in the form of goodwill. He would have to build that from scratch at United.

He would likely be paid a good deal more by the Red Devils and might even have a bigger operating budget, but it is not the no-brainer many United fans seem to think it would be. Indeed, the conversation on Twitter featured a good deal of debate as to whether he would come.

Even asking this question is yet another moment in the post-Ferguson era when United fans have to deal with the harsh, painful realities of life without him. Just 18 months into a superstar manager's reign, to even be talking about future managers shows how much things have changed.

In many ways, the best outcome would be for Mourinho to defy expectation and stay at Old Trafford for the long haul. That always seemed like an outside bet, and nothing that has happened so far has changed that.