If only there could be many more snubs like that. On Monday, a leak from the White House suddenly made it clear that there would be no summit between the European Union and the United States in late May, as had been widely anticipated.

It’s a great service that Barack Obama rendered to Europeans. This humiliation probably convinced a few more of the obvious need to finally get their acts together and be more united on foreign policy if they want to have a say in the world — or just be taken seriously.

What makes the rebuff particularly stinging is that Europeans know Mr. Obama is right; they know he would welcome and regularly meet a senior European Union official, or even several (provided they don’t rotate every six months), who would actually talk for all of Europe. (Not to mention their dashed hopes in the Lisbon Treaty, which was supposed to enhance their diplomatic credibility.)

In fact, much of Europe’s progress in foreign policy in the past two decades came after similar moments of frustration, humiliation and antagonism.