Editor's Note: (Anand Menon is professor of European politics and foreign affairs at King's College London. The opinions expressed in this article belong to the author. )
(CNN) For more than 60 years, European integration has proceeded apace, often muddling through when apparently insoluble problems assailed it.
Now, though, things look different. For the first time, a member state has decided to leave. And the particularly toxic blend of complex problems and decreased room for compromise make it impossible to see how all of the issues confronting the bloc can be resolved without undermining the principle of union.
On Wednesday, Jean-Claude Juncker, president of the European Commission, delivered his annual State of the Union speech. On Friday in Slovakia, the European Council meets for the first time without Britain to discuss what the European Union does next.
Europe's State of the Union is, of course, nothing like its American namesake. It is delivered by a man with the ability to suggest rather than the power to act. A man who speaks in the name of an institution that is partly the cause of -- and partly the answer to -- the dilemmas that Europe must resolve.
These dilemmas range from the question of how to deal with migrants who have arrived on the continent, to the need to resolve the lingering problems of the eurozone; the security concerns stemming from ISIS in the south to Russian aggression in the east. And, of course, the recent problem of populist politics afflicting all European nations, which may yet have significant consequences in forthcoming elections.
For many of these problems, the solutions are European, but because of the EU's lack of authority over its constituent member states, they require agreement between national capitals.
Take migration. On one level, it makes perfect intuitive sense to argue that member states should share in the burden of taking care of those who have arrived in Europe seeking a better life. On the other, it makes less sense to a Polish politician faced with growing resentment at what is seen as excessive EU interference in national life to give in to demands for a collective response. And the angrier the fight, the more oxygen is provided to the populists who thrive on opposition to European integration.
This is the reality of European integration today: marooned uncomfortably between the European collaboration that member states feel they need and the national control they crave nonetheless.
Juncker, to his credit, recognized as much when delivering his annual address this week.
He focused, both explicitly and implicitly, on the need to rally member states to the cause. Never, he correctly observed, has there been so little common ground between national capitals and never have they been so weakened by populism. And crucially he recognized that only if member states were willing to go along with what he suggests would any action be possible.
His words were calculated to appeal directly to some of those national capitals -- for example, his support for reform of the posted workers directive was a sop to a French government that has threatened simply not to apply it.
"The EU Commission," he was in effect saying, "is on your side."
Which is nice. Unless you are a leader of a European country, trying to find a way to confront a range of tricky problems in the real world. The difficulty that the heads of state and government now face is of how exactly to reconcile that chasm between the collective action that the union needs, and the domestic imperatives to which national leaders tend to respond.
The fundamental problem for those meeting in Slovakia is that difficult choices will have to be made that will impose greater costs on some than on others. Resolving the eurozone crisis is a case in point: Should the debtors pay for their alleged misdeeds, or should solidarity imply a sharing of risk? Either way, one set of voters will be left feeling put upon by the EU.
Dealing with the migrant crisis, as we have seen, will involve difficult choices about how and whether to help those southern countries bearing the brunt of the problem, and how to distribute the burden among those willing to lend a hand.
And into this heady mix has now been added the issue of Brexit. On one level, it is simply another toxic issue to add to the pile, thereby further consuming the limited bandwidth of national leaders at their European summits. On another, it feeds into pre-existing problems.
It will be harder to solve the problem of Italian banks without the City of London in a capital markets union. Equally, it will hardly be straightforward to persuade the East European states that Britain should enjoy market access while being able to prevent their nationals from seeking work in the UK.
An optimist might assert that European integration thrives on crises -- that the challenges Europe confronts, combined with a desire to illustrate the continued vitality of the union following the British referendum, will conspire to render national leaders more willing to ignore short-term pressures and make the sacrifices that any effective outcome will require.
I find it hard to concur. Behind the fine rhetoric that will doubtless come out of the Slovak capital, the fundamental issues will remain unresolved. The sacrifices will not be made, and Europe will continue to muddle through. The constraints of national politic will triumph over the demands of transnational unity.
The EU will stumble on, no doubt. But the problems it faces will only become more severe.