The Justice Department won't pursue contempt charges against the witnesses who invoked Executive Privilege.

Any alternative?

Congress has another route to enforce its will, an inherent power of contempt. But that has not been used since early in the 20th century. It has long been deemed unwieldy in the modern era as it entails Congress stopping all work to hold its own trial and imprisoning any offenders in the basement of the Capitol.

"Unwieldy," i.e., too bizarre to do.