Inside prosecutions of presidents and other high-ranking administration officials can arise in two ways. The first is what we might call the “organic” route: FBI agents and/or Justice Department attorneys undertake an investigation within the scope of their normal duties that leads them to suspect wrongdoing by the president or other senior administration officials. This is what happened in the Agnew scandal. Three assistant U.S. attorneys in Maryland began looking into rumors that local Baltimore officials were taking bribes. The trail soon led them to the sitting vice president, and then-Attorney General Elliott Richardson allowed them to keep the case. The second type of inside prosecution is what we might call the “inside special prosecutor” model: the president or attorney general (or in the event of recusal, deputy attorney general) assigns an official already within the federal government to investigate a matter involving administration members. This is what happened in the Valerie Plame affair, when then-Deputy Attorney General James Comey named the U.S. attorney in Chicago at the time to probe the Bush administration’s apparent leak of a CIA officer’s identity.
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