An email indicating Hillary Clinton intervened on behalf of a friend of her son-in-law, Marc Mezvinsky, predated what appears to be a period of success for the mining company in question.

The email, which was made public at the end of last month by the State Department, has touched off a new round of criticism from observers who note the growing number of instances in which the lines between Clinton's friends, foundation and diplomatic business were blurred. It also highlights a major flip-flop on offshore drilling, a practice she pushed Congress to facilitate in 2012 but is now campaigning against.

While there is little evidence that Mezvinsky's request resulted in direct favoritism for the firm at the heart of the controversy, the company's notable success within two years of its founding raises questions about how it was able to grow so quickly.

Harry Siklas, a friend of Mezvinsky's, asked the husband of Chelsea Clinton if he or his "better half" could connect him with someone in Hillary Clinton's office so Siklas could lobby on behalf of Neptune Minerals, a deep-sea mining company, in May 2012.

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