Biden personally vetoed the delivery of jets for fear of provoking Putin. The bigger problem is the message this fiasco sends to Mr. Putin about NATO. The essence of credible deterrence is making an adversary believe that taking certain actions will draw a response. By so ostentatiously not sending the fighters, and saying the reason is fear of escalation, Mr. Biden is telling the Russian what he doesn’t have to worry about. Instead of deterring Mr. Putin, Mr. Biden is letting the Russian deter the U.S.