The topic under discussion was whether the West—in the absence of any intention to intervene directly in Syria—should supply arms to the outgunned rebels fighting President Bashar al-Assad. Sherman, pressed hard on the issue, was forced to use the full arsenal of diplomatic vernacular to say “no” while maintaining that the United States was deeply concerned about the atrocious situation on the ground.

She sounded believable on both counts. She was visibly torn, but her statements were an exercise in caution, passivity, and the carefully crafted abstention that only seasoned diplomats can produce. She was very professional in saying “no,” but there was also just enough genuine pain in her performance to avoid appearing cold.

In other words, she was the epitome of the U.S. foreign policy posture in President Barack Obama’s second term.

Vaïsse, in contrast, argued so fervently in favor of arming the insurgents that no one in the room could remember when old Europe had last looked so young and ready to act. At least France, after Libya and Mali, looks decidedly rejuvenated these days. Vaïsse argued that France would also prefer a negotiated solution for Syria, and that it had tried—in various ways, both inside and outside the UN Security Council—to reach one.

These efforts, however, had led to nothing, and it was now time for plan B. Together with the UK, he said, France was considering sending weapons to some rebel groups, despite the recently prolonged EU embargo on arms deliveries to Syria.

Regardless of whether one believes such a plan is a good idea, the scene is of high significance. It is important less for the robustness of France’s position than for the defensiveness of America’s.

While everyone knows that unilateral French interventionism would not be a game changer in world affairs, unilateral American passivity would. So I asked myself afterward: Is this the America that Europe wants? Is this the America that Europe needs? The answer to both questions is—unfortunately—yes.

Most Europeans, with few exceptions (I am one), have always wanted a United States that sounds like Wendy Sherman sounded in Brussels. One that stays out of problems instead of feeling responsible for solving them. One that believes that the use of force is not the solution to every conflict. One that thinks it cannot afford to be the world’s policeman.

Europeans who follow this line of thinking feel encouraged by examples like the disastrous failure of the U.S. intervention in Iraq. They now dismiss as arrogant and gravely mistaken the idea that the United States should be a global provider of stability. That this was and is an epic miscalculation does not occur to most Europeans. They have no idea what it would mean if they really were to get a passive, non-interfering United States.

That brings us—in a slightly convoluted way—to why this is the kind of United States that Europe might actually need. It may well be that only the pain of America’s absence will bring the old world to its senses. Perhaps—as Europeans start to realize that, without U.S. help, global peace and stability are much less stable—they will start to invest in the intellectual, political, diplomatic, and military tools to become a more self-sustained, decisive player in the world.

It seems that, very slowly, this lesson is sinking in with part of the European audience. But the lesson comes at a difficult time, of course, as the resources to make these investments are scarce, and will likely get scarcer over the next few years.

It would be so much better if Europeans could come to this important conclusion without Wendy Sherman’s unintended school lesson (or the very much intended one given by former U.S. secretary of defense Robert Gates before her).

The real lesson here is that Europe needs to invest in its instruments because it needs to be both more self-sufficient and more useful as a partner for the United States. In the end, U.S. passivity and European weakness are two sides of the same coin. It is the global liberal order, Western democracy, stability, and open societies that will suffer otherwise. Europe has much to lose in the emerging new world, but very little capacity to defend it.

As things stand, Europeans will inevitably suffer more pain until it hurts enough for them to finally do something about it. It may be cynical to hope that pain will bring about a reassessment of the situation, but that is better than no hope at all.

Europeans should take a careful look at Wendy Sherman’s pain over Syria if they want to understand that the time for outsourcing the protection of their own strategic interests is fast coming to an end. It won’t be enough for the French alone to realize that.