Economic sanctions are a flawed and double-edged weapon, but, short of armed force, they are the only tools at the disposal of the West to make President Putin and his revanchist-ruling clique understand that breaking the rules of international behavior carries a cost, and, further, that there can be no business-as-usual when Russia carries out armed aggression against a sovereign state while enabling proxies in eastern Ukraine who shoot down an unarmed passenger plane.

Europe’s readiness to strengthen its earlier response — which has consisted mainly of restrictions on individual Russians — and to join the United States in striking at the Russian economy shows that Europe’s leaders have now grasped the magnitude of Mr. Putin’s threat. It shows also a commendable willingness to confront that threat despite the difficulty of coordinated action by 28 European Union members, Europe’s heavy dependence on Russian natural gas, and the potential cost in lost jobs and contracts.

This change of view makes all the more troubling France’s continued determination to deliver at least one of the two Mistral-class warships it is building for Russia for 1.2 billion euros, or about $1.6 billion. The Mistral is not heavily armed, but it is a serious military asset as a forward command post and helicopter carrier. It is, in short, a formidable weapon, and the very idea that France is building two for Mr. Putin at this time is deeply troubling.

President François Hollande of France and other French officials have reacted angrily to American and British calls for the deal to be suspended. Prime Minister David Cameron of Britain has been especially sharply assailed in France for criticizing the French while keeping Britain’s doors open to Russian oligarchs who park a lot of their loot in London. Certainly Britain cannot be exempt from making sacrifices in any future round of sanctions; nor Germany, with its extensive exports to Russia, nor any other European Union member. But financial sacrifice is one thing; arming Russia is another. That is what the French should focus on at this juncture, not the supposed slights of their allies.

At this point, it appears likely that France will go ahead with the delivery of the first Mistral, the Vladivostok, in October. But Mr. Hollande has left open the possibility of at least delaying the second one, which is due for delivery late next year. One warship less may not hurt Mr. Putin as much as economic measures that shrink his economy and hurt his cronies, but a decision by France to suspend the deal would encourage other European countries to accept whatever sacrifices future sanctions might entail. It would also make a powerful statement about Western resolve not to appease Mr. Putin — and about French honor.