In what is the strongest sign yet of the damage that plunging crude prices are doing to the U.S. oil industry, drillers idled more rigs last week than they have at any point since 1991. Oil rigs fell by 61 to 1,421, Baker Hughes Inc. (BHI) said on its website today, extending the five-week decline to 154. The 2014 peak was 1,609. It was the largest drop since February 1991, which also followed a tumble in prices before the start of the Persian Gulf War . The price of U.S. benchmark West Texas Intermediate oil has plunged by more than half since June, imperiling a shale boom that has brought the nation closer to energy independence than it has been in almost three decades. U.S. drillers laid down the most rigs last quarter since 2009 as the Organization of Petroleum Exporting Countries and the rest of the world’s suppliers […]