Russia could further undermine Europe's energy security long after it cuts off gas supplies, if Moscow begins to more aggressively target the continent's maritime oil and gas industry. On Sept. 26, the Norwegian Petroleum Safety Administration warned of potential ''deliberate attacks'' after energy companies reported multiple cases of unidentified drones flying near offshore oil and gas installations. Just a few hours later, officials in Denmark warned they had found a gas leak along a section of the Nord Stream 2 pipeline off the coast of the Danish island of Bornholm. The following day, the Swedish Maritime Administration announced it also detected two gas leaks on the Nord Stream 1 pipeline in a nearby area. Russia is widely believed to be behind the recent attacks on the Nord Stream pipeline systems, which are both operated by the Russian gas giant Gazprom. But while the Kremlin has not yet shown an intent...