Obama Purging Attorney Who Initiated Charges Against Black Panthers?

Christopher Coates, the head of the DOJ's Voting Division that initiated charges against those Black Panthers who were intimidating White voters in Philadelphia, has been replaced. He has been subpoenaed by the US Civil Rights Commission in order to explain why the DOJ later dropped many of the charges against the Black Panthers. I wonder if this is a way to sully then name of Christopher Coates before he testifies in order to spin anything he says as the testimony of a disgruntled employee. It is also possible that he was going to cooperate with the subpoena (something he was illegally ordered not to do by the Obama administration) and this is the Obama administration simply retaliating. It is the Chicago way after all.