Glencore (LSE: GLEN ) hasn't been able to catch a break – only weeks after dealing with two other major problems on its plate, its share price tumbled with news that the US authorities have subpoenaed the Swiss company, demanding documents on its operations in the Democratic Republic of Congo, Venezuela and Nigeria as part of a corruption probe. When the news broke, Glencore lost over 14 percent of its value on the London Stock Exchange as the news sent shivers through investors.