TOW (& Answer)...

The question was what is Congressional immunity?  To answer: “The Constitution shields members of Congress from lawsuits of criminal charges that relate to their legislative duties.”  This protection was planned to keep Congress independent from the legislative branch.  

The question (& answer) were found on p. 215 of Congress A to Z edited by David R. Tarr and Ann O’Connor and published by the Congressional Quarterly in 1999.