The draft agenda for the upcoming European Council meeting of 16-17 December currently runs to four broad issues. The discussions are, in order, on migration; on the President's report on the Economic and Monetary Union; on the deepening of the single market, and finally, on the UK referendum. But as members of Jean-Claude Juncker's office struggle through the security lockdown to reach the Commission offices, it would be surprising if they were not considering a realignment of that agenda towards the security crisis affecting western Europe.
That predicted shift crystallises the growing bind that David Cameron is in with his renegotiation. His discussion on the referendum in December was meant to be the touchpaper for a confected row about Britain's EU membership of the European Union, to demonstrate to an increasingly sceptical country that he is willing and able to push hard for change.
Terrorism aside, his plan to change Britain's membership was already on the skids. He has already had to concede that treaty change before 2017 is impossible, and an earlier Council discussion on the same issue had to be wedged around a heated all-night discussion on migration in June. Cameron knows that, in effect, negotiations have to be wrapped up by the end of next year to give both the French and the Germans breathing room for their national elections, which fall due in 2017. Meanwhile, his backbenchers are increasingly restless, and the 'Leave' campaigns are gaining confidence and share of voice in Britain.
Now that the security situation in Europe has worsened so dramatically, his bid to deliver a genuinely new-found relationship with Europe is looking ever dicier. As the citizens of Paris come to terms with the attack on their city, and as Brussels remains in stark lockdown, it is increasingly unlikely that a British tantrum is going to be met with sympathy and understanding. This is not to forget, of course, that the hundreds of thousands of migrants and refugees marching towards western Europe have not vanished; indeed, in the words of former Foreign Secretary William Hague,
the migrant crisis is a mere gust of the hurricane that will soon engulf Europe.
So Mr Cameron is in an increasingly Gordian fix. He needs his row on 16 December, but even if he gets it, it is likely to be brief and extremely limited in scope - just like the terms of his renegotiation. It will almost certainly not be enough to satisfy his critics back home.
But he knows that, after Paris, terrorism will remain at the top of the agenda for months, as Europe struggles to better integrate its intelligence and security apparatus in order to contend with the threat. British security is integral to this cooperation, so he will be left in the confusing position of strengthening relationships with Europe in some areas while trying to weaken them in others. And this will have to be done in the margins of summits with much bigger issues on the agenda than just bolshy old Britain.
Even Mr Cameron's most hostile backbenchers could not expect him to have predicted such a dramatic worsening of the continent's security problems, or the sustained response that is clearly now required. But now he has laid out his renegotiation areas, and set an extremely short timetable to achieving something meaningful, he finds himself hamstrung by them. And the longer the lockdown goes on in Brussels, the more European minds will be focused anywhere but Britain's tinkering with European Union rules. Mr Cameron has so far proved himself above all to be a politician of exceptional good fortune. He must be hoping for more of the same come December.