Participation served President Putin's ambitions to rebuild Russia's influence in the Middle East. Withdrawal is aimed at punishing the U.S. for its repeated attacks on Russia's energy interests through sanctions, which have stifled Arctic offshore exploration and shale development, prevented the completion a gas pipeline to Europe under the Baltic Sea, and targeted the Venezuelan business of Russia's state-oil producer Rosneft. Saudi Arabia led OPEC in a war on shale in 2014, when it introduced the pump-at-will policy. It failed then, capitulating as oil prices collapsed a year later. But U.S. producers from Exxon Mobil Corp. to Continental Resources Inc. are already being hammered and now may be a more auspicious time to launch an attack. Even if it fails again, Russia intends to make sure that U.S. oil companies share the pain of the collapse in oil demand. Saudi Arabia appears wiling to help it.