[dmvdoug]

It's vanishingly rare, of course. Part of the problem is how does Congress get classified information from the Executive Branch? The latter has to turn it over. Cooperation between the two is necessary. If Congressfolk routinely read classified information into the record, cooperation would vanish. If Congressperson Blip made it a habit to run to the floor everytime s/he received anything with classification markings, Congressperson Blip would find that supply drying up faster than rain in a desert.

But it is an ultimate recourse Congresspeople have, should they come into possession of classified information they are afraid will be deposited into the memory hole, like Senator Gravel did with the Pentagon Papers.