I believe it was either written or anthologized by Spider Robinson.
Close. It was entitled The Return of William Proxmire and was by Larry Niven...likely the reason TB recalled it as an excellent yarn. It appeared in Requiem I believe, [Tor; 0-312-85168-5] and originally ran in What Might Have Been? Volume I: Alternate Empires edited by Greg Benford and Martin Greenberg for Bantam [Spectra] from 1989.
I wonder what H. Beam Piper thought of R.A.H's writing....
-archy-/-
Yup---the reason I thought it was anthologized by Spider was because he had written so much additional commentary/content for "Requiem", especially "rah! rah! RAH!" stuck in my mind along with the Proxmire yarn.
Oh yeah, another Niven tribute to Heinlein: "Robert Anson" (and his wife Virginia)whose ID "declares him to be the US Navy's oldest Lieutenent(jg)", as a member of the "Threat Team" of SF writers the Government assembles in Cheyenne Mountion to consider responses should the alien spaceship detected entering the Solar system should be hostile. (in Niven & Pournelle's Footfall (US Army Sergeant's observation on SF Writers "most passengers don't try to talk over helicopter engine noise. These people were winning")