Because France has had such a crucial role in creating the European Union, this second dimension should not be underestimated. Whether from the right or the left, postwar French leaders have constantly pushed to take Europe further. Europe, in the French vision, is not only an ideal: It is an instrument of power on the world scene. Ever since France first became a great power in the 13th century, it has had the ambition to remain one. After World War II, France saw Europe as a way to access power again. General Charles de Gaulle got France a permanent seat on the United Nations Security Council and made it a nuclear power, but the European construction brought it two more benefits: size — which mattered in a bipolar world — and a reining in of that other formidable European power, Germany…

How will this development play out in the French psyche? In the collective soul-searching that has begun within the European Union after the Brexit earthquake, a strong emphasis has rightly been put on the bloc’s austerity policies and on Brussels’ encroachments. Now comes the naked truth: For the past 10 years, the European Union has failed to deliver on the main objective it was set up to achieve: shielding its citizens from insecurity. Over the past few days, European leaders, in a state of shock, have hastily identified three priorities on which to focus if they want to save their union: security, migration and economic growth.

This is a good start, but something is still missing. Well-known divisions among the 27 over these issues will be overcome only if European citizens regain a sense of the political and historical mission of the European idea. Why are they together? The level of emotions expressed in Europe in reaction to the British vote has shown that the feeling of belonging to a common entity, or of being excluded from it, is surprisingly strong, notably in the young generation. Maybe that can even look like something called a European identity. Maybe a new political idea, more attuned to 21st-century realities, can even be built upon that identity. This will be the best way to counter Ms. Le Pen’s argument that Europe is a “prison of the peoples.”