Sen. David Vitter wants to put the klieg lights on any member of Congress who decides that certain staff members are not “official,” a maneuver that would exempt the employee from entering a health exchange tied to Obamacare as mandated by the 2010 law. Mr. Vitter, Louisiana Republican, filed the Show Your Exemption Act on Thursday to force lawmakers to reveal how they designate each of their staffers. Sen. Chuck Grassley, Iowa Republican, wrote an amendment to the Affordable Care Act that placed members of Congress and their staffs in the state-based insurance markets, or exchanges, set up by the...