I wrote in October that a time will come when the interests of the eurozone will not only collide with those of the non-eurozone, but with the EU itself. We are now at that point. On Thursday night, Angela Merkel and Nicolas Sarkozy clashed with David Cameron in a familiar Britain-versus-the-rest diplomatic standoff. That itself is not new. But a determination to go outside the treaty to overcome the disagreements adds a new dimension to this long-lasting dispute.