Russian President Vladimir Putin, frustrated by his bogged-down war in Ukraine, is trying to intimidate the European nations that — given President Donald Trump’s severe cuts in aid to Kyiv — are now Ukrainians’ main military, economic and diplomatic supporters. A few of the many examples: an explosive-laden drone found at the airport in Leipzig, Germany; vital undersea cables cut or damaged in the Baltic Sea; parcels exploding at logistics facilities in Germany, Poland and the UK; a failed arson attack at a Czech bus depot; a Polish railway damaged by explosives; and a steady increase in the intensity of cyberattacks against North Atlantic Treaty Organization members. While Moscow of course denies involvement, Western intelligence and law-enforcement agencies have convincingly attributed these attacks to the Kremlin, and in some cases obtained indictments and convictions. Such incidents are known as hybrid or gray-zone warfare. The idea is to undertake sabotage and initiate disruptions across a wide spectrum of civilian targets that fall short of actual warfare, and in a way th