The best place to begin when pondering David Cameron’s future is with the electoral facts.  He has fought two general elections, forming a coalition the first time round and gaining a majority the second (thus becoming the first Prime Minister in a hundred years to see his vote share increase at an election).  He has also won two referendums, and may well triumph in a third.  By my reckoning, he could reasonably claim to be the second most electorally potent Conservative leader since the Second World War – since he has fought more general elections than Eden and Macmillan, who each won a solitary one, without losing any of these he has contested.  By Matt Smith’s calculation, he has the second best record in a hundred years.

Complain if you will that he bungled the 2010 election, in which Steve Hilton’s manifesto pulled one way and George Osborne’s instincts another, and that without Lynton Crosby’s remorseless seat targetting he would probably have fallen short in 2015, too.  But if it is fair to call him a lucky Party leader it is also fair to add that effective Party leaders make their luck.  Or one can take a more elevated view, and argue that what matters more than his record at the polls is his record in office.  But one would truly have to hate him to claim, as a Tory, that it has been a bad one, and that his premiership has been worthless.  Yes, there have been dire blunders in Government (the 2013 Syria vote, the “Omnishambles” budget, the 2010 health bill).  The deficit still looms.  And, yes, there have probably been even worse errors in party management.  These can be crystallised into a single point: the influence over policy and patronage of one man, George Osborne, was arguably too big from the start and has certainly got bigger since.

But the broad picture remains the same.  Since the fall of Margaret Thatcher and before the rise of Cameron, the Party fought four general elections, and lost three of them.  It also experienced five leadership elections, two of them involuntary.  The Prime Minister has helped to oversee an economic recovery – the biggest tick in his Chancellor’s credit column – and a sweeping programme of public service reform at least as big as Thatcher’s.  The only rational conclusion for any Tory to draw is that he deserves to stay in Downing Street for as long as he likes – for all the strategic waywardness of this constistent chameleon.  But reason does not always master hatred, and a handful of Conservative MPs truly hate him.  Hence the chatter this morning about a leadership challenge immediately after the referendum.  All it is likely to do is to distract attention from the referendum at exactly the moment when, thanks to purdah, Leave now at last has a chance to fight the campaign on a level playing field.

That the field has not been even, Cameron’s extreme critics would reply, is exactly the point – and why he should go, even if Remain wins.  None the less, Party-harming talk has come from both sides.  The Prime Minister has questioned his critics’ patriotism.  They have questioned his honesty.  And it was always likely, on reflection, that the toxic interplay of an EU referendum now and a leadership election before 2020 would see a rhetorical race to the bottom.  Passions seethe on both sides.  Cameron is bound to take the Leave campaining of, say, Michael Gove, very personally indeed: after all, his former friend is now striving in effect to oust him from Downing Street in short order.  And the Prime Minister clearly believes in the cause of Remain.  That this has always been so is a large part of the reason why many Leave campaigners are so enraged, concluding that he would never have countenanced backing a Leave vote – and that his renegotiation, the foundation on which his case for Remain is built, is a conjuring trick.

Those who want him out of Downing Street in short order are on firmer ground when they point to the way in which the Government has abused pre-purdah – all the way from the misuse of the civil service through dodgy dossiers to favours doubtless hinted at in due course.  If Remain indeed does win, watch the peerage list that will follow.  But a referendum of this kind was never likely to be fought under Queensbury Rules, and many pro-Leave MPs will not return to Westminster determined to oust Cameron in consequence.  Rather more serious for the Prime Minister is a problem that he has actually created for himself.  He was under no obligation to say, before the last election, that he would not contest the next one.  But he did.  The consequences were bound to be destabilising.  If Leave wins, Cameron will presumably continue in Downing Street until a Conservative leadership contest is completed.  But if Remains succeeds, he faces a quite different but almost as fundamental problem.

In a nutshell, this is that no pledge by him to stay in Number Ten until 2019 can be entirely convincing.  The Prime Minister wants the Chancellor to succeed him.  If Remain wins, he might therefore suddenly quit at a moment between now and 2019 that suited his friend – or another pro-Remain Cabinet Minister who makes his way through the pack.  (Stephen Crabb, say.)  In any event, the brutal truth is that the Government is under siege in the Lords and has no real majority in the Commons.  These are not circumstances that would bolster Cameron even at a time more benign than the wake of a uniquely divisive referendum campaign.  If the presumption on paper is the Prime Minister should stay in post until 2019, the reality in practice is that this may turn out to be impossible.

What would make his survival more likely and the Government’s prospects more bright in the event of that Remain vote?  Perhaps three things.

First, for Cameron to reject a revenge shuffle and hold a unity one – an integral part of which would be making Gove Deputy Prime Minister de facto if not de jure, a view shared by two in three of our party member readers.

Second, this site believes that on balance it would be best for the Chancellor to move to the Foreign Office, but at the very least power should be shared more widely with the top Cabinet team.  To appoint an MP as Party Chairman (we recommend Michael Fallon or Jeremy Hunt) would be a sign that this is happening.

Finally, the Government has no alternative but to recognise that its potency in Parliament is limited, that it will need cross-party consent for most of its legislation (a conclusion we draw with reluctance) and that planning for the 2020 manifesto begins now.  After all, it’s not impossible that the Party’s share of the vote will rise further in four years’ time – if the will to find a post-referendum settlement is there on all sides.