It’s official—oil is in a bear market following Tuesday’s 2% fall, taking prices 21% below late-winter highs. The Organization of the Petroleum Exporting Countries’ high hopes for crude have been shredded by the sharp claws of resurgent U.S. shale. It’s been a nasty few weeks for oil investors. The International Energy Agency last week cast doubt on OPEC’s ability to do “whatever it takes” to drain massive global crude stocks,…