From the Prime Minister’s point of view, there is just one way to win the EU referendum, but plenty of ways to lose it.
If it all goes according to plan, the outcome gives him a winning hand:

• The United Kingdom votes by a decisive margin to stay in the European Union
• The UK government’s push for reform gains momentum around the Union and bolster’s Cameron’s influence
• The Eurosceptics in the Conservative party are silenced
• UKIP is fatally holed below the waterline and vote begins to melt away
• The Prime Minister has secured a smooth glide path to Camerexit, at a time of his own choosing

There would be nothing like a hands-down win to turn what was Mr Cameron’s considerable gamble into something resembling an act of statesmanship.
But that’s if it all goes according to plan.

The trouble is there is just one way of winning this thing, but many more ways of losing it. Then the aftermath looks very different.
For the Prime Minister, he needs a fortuitous alignment of the political planets to pull this off. His renegotiation will have to look both significant and meaningful.

He will need a campaign that has a carefully choreographed and positive message. He will need to be fortunate in his opponents. He will have to be lucky in his timing, and hope that his referendum does not coincide with another European crisis. He will need the voters to stick to the issue and not redefine the question on their own terms. He will need to de-couple the EU from its ‘establishment’ identity and recast it as something deserving of positive support. And then he needs a big turnout and a win by a decisive margin.

So not too much to ask for.

And there are so many things that could upset the plan.

His renegotiation may be effectively cast as insignificant, not just by ‘out’ campaigners here but, more dangerously, by leading figures around the Union. There are plenty capable of a damaging slip of the tongue. Then the new terms of membership dissolve as an issue in the debate; instead it slides back to a basic in or out anyway, as the pretext for the question disappears.

The timing could prove unfortunate. ‘Events, dear boy’ could intervene one again. There are plenty of potential candidates for disruption: a renewed immigration crisis; another twist in the euro zones’ travails; a controversial EU Commission proposal; a further economic slowdown. Any one could energise the ‘outs’ and push the ‘ins’ onto the defensive.

The ‘in’ campaign stumbles. Making the case for the status quo isn’t too tough when it’s actually something quite new, as in the 1975 campaign. But when it’s in defence of an arrangement that is 50 years old and which has been a rocky affair most of time, the going could be a lot tougher, and the sight of all the establishment political leaders riding to the rescue of an unloved institution could just make the case fall apart.

The risk is that any of these developments, or some combination of them, could lead to any one of a number of ways for Mr Cameron to lose.

The result could be a clear vote for ‘out’. Cameron’s proposition is rejected and his premiership comes to an abrupt end. The United Kingdom government is left carrying his hospital pass, uncertain what to do next, as markets tumble and Mr Farage rides in triumph.

The result could split the United Kingdom, with England voting ‘out’ and Scotland ‘in’. Not only will the EU membership question be unraveling, but so will the UK, as Scottish independence gets its strongest ever shot of adrenaline.

This is going to be a long campaign and the risk is that by the end of it, we have one seriously bored electorate.

The result could be a narrow vote for ‘out’, but on a low poll. The analysts will quickly work out that a major switch of direction in Britain’s international arrangements is about to happen, thanks to the expressed will of something like 25% of the electorate. Too many figures across political and business worlds will refuse to accept that this is a done deal.

The result could be a narrow vote for ‘in’ but on a low poll. The result rescues the Prime Minister but the debate is far from shut down. It could be Indyref all over again: a brief period of relief, eventually followed by recriminations, renewed argument, accusations of bad faith, and more grumbling about the UK in the inner circles of the Union.

This is a gamble of the Prime Minister’s choosing. He needs not just a win, but a big win – a high turnout, certainly over 60%, and a winning margin of over 15 points – and his strategy from now on will be aimed at pulling off just that.

If, on the other hand, he ends up with any one of the various ways of losing he will have unleashed a potentially painful era of brexistential doubt.

And his premiership will be more likely to end ingloriously.