BERLIN — An idea, once unthinkable, is gaining attention in European policy circles: a European Union nuclear weapons program.

Under such a plan, France’s arsenal would be repurposed to protect the rest of Europe and would be put under a common European command, funding plan, defense doctrine, or some combination of the three. It would be enacted only if the Continent could no longer count on American protection.

Though no new countries would join the nuclear club under this scheme, it would amount to an unprecedented escalation in Europe’s collective military power and a drastic break with American leadership.

Analysts say that the talk, even if it never translates into action, demonstrates the growing sense in Europe that drastic steps may be necessary to protect the postwar order in the era of a Trump presidency, a resurgent Russia and the possibility of an alignment between the two.