America’s emergency oil stockpile has fallen below 300 million barrels for the first time since the Strategic Petroleum Reserve was filled in the early 1980s. Now, some energy experts are warning that the problem may go far beyond simply having less oil available during the next crisis. The rapid drawdown could threaten the underground salt caverns that hold the crude, potentially reducing how quickly the United States can respond to another major supply disruption. The warnings come as the U.S. releases 172 million barrels from the Strategic Petroleum Reserve, or SPR, in response to supply disruptions caused by the Iran...