John Durham has a stellar reputation for investigating corruption. Some fear his work for Barr could tarnish it.

When the U.S. government needed a prosecutor to ferret out corruption in its own law-enforcement and intelligence ranks, John Durham was its go-to guy. The longtime prosecutor helped exonerate men wrongly convicted on murder charges, exposed an FBI agent tied to one of Boston’s most notorious gangsters and dug into the CIA’s destruction of video tapes thought to show foreign detainees being tortured.

But some of Durham’s actions in his latest high-profile assignment — examining the FBI’s 2016 investigation of President Trump’s campaign — have sparked a debate in Washington about whether he is even-handedly assessing possible wrongdoing, or carrying out a conservative political errand.

Last week, after the Justice Department inspector general released a report concluding the bureau had adequate cause to open the investigation into possible coordination between the Trump campaign and Russia, Durham issued a remarkable public statement registering his disagreement.