The stakes for McCabe’s appearance, however, are particularly high. The former No. 2 at the FBI is entangled in a separate criminal investigation stemming from an earlier report from the inspector general’s office that concluded he lied to internal investigators. McCabe has steadfastly denied wrongdoing, but any congressional testimony he provides could have serious implications for his criminal case.

“Mr. McCabe is willing to testify, but because of the criminal referral, he must be afforded suitable legal protection,” Bromwich wrote to Grassley. “This is a textbook case for granting use immunity. . . . If this Committee is unwilling or unable to obtain such an order, then Mr. McCabe will have to no choice but to invoke his Fifth Amendment privilege against self-incrimination.”

If McCabe invokes his Fifth Amendment right instead of answering certain questions, it could set up a contentious confrontation with lawmakers. They could serve him with a subpoena and if he continues to refuse to testify, lawmakers could pursue a contempt resolution against him and refer the matter for prosecution by the DC US Attorney’s Office or enforce the subpoena through civil action in federal court.