I think that this New Yorker profile of Carson may be the origin of this blog's name (I have a compilation of New Yorker biopieces and Carson's is included):

Characteristically, although he is surrounded by the likes of Jack Lemmon, Roger Vadim, Michael Caine, James Stewart, and Gene Kelly, he spends most of the evening locked in NBC shoptalk with Fred de Cordova. De Cordova has just returned from his European safari, which has taken him through four countries in half as many weeks. The high point of the trip, de Cordova tells me, was a visit to Munich, where his old friend Billy Wilder was making a film. This brings to mind a recent conversation I had with Wilder in this very living room. He is a master of acerbic put-downs who has little time for TV pseudostars, and when I mentioned the name of Carson I expected Wilder to dismiss him with a mordant one-liner. What he actually said surprised me. It evolved in the form of a speech. “By the simple law of survival, Carson is the best,” he said. “He enchants the invalids and the insomniacs as well as the people who have to get up at dawn. He is the Valium and the Nembutal of a nation. No matter what kind of dead-asses are on the show, he has to make them funny and exciting. He has to be their nurse and their surgeon. He has no conceit. He does his work and he comes prepared. If he’s talking to an author, he has read the book. Even his rehearsed routines sound improvised. He’s the cream of middle-class elegance, yet he’s not a mannequin. He has captivated the American bourgeoisie without ever offending the highbrows, and he has never said anything that wasn’t liberal or progressive. Every night, in front of millions of people, he has to do the salto mortale”—circus parlance for an aerial somersault performed on the tightrope. “What’s more”—and here Wilder leaned forward, tapping my knee for emphasis—”he does it without a net. No rewrites. No retakes. The jokes must work tonight.”

...I'm sure I've seen the term elsewhere. It takes a few iterations for something to lodge firmly in my head. This was definitely one of the iterations. It's rare for me to (re-)find them.