The Russiagate special prosecutor has taken on a tough case: indicting Igor Danchenko, the principal sub-source for the discredited “Steele dossier,” which was penned by former British spy Christopher Steele and commissioned by the Hillary Clinton campaign to smear her GOP rival, Donald Trump, as a Kremlin mole. The peddling of a false narrative of Trump collusion with Russia was a product of the Clinton campaign and the FBI. Voluminous reports by the Justice Department’s inspector general have demonstrated that the bureau’s hierarchy was seized by anti-Trump animus. The FBI knowingly allowed itself to be fed partisan opposition research that...