[1]: https://www.smh.com.au/entertainment/art-and-design/stop-cla...
[2]: https://www.theguardian.com/culture/2000/jul/31/artsfeatures...
This feels like a rabbit hole best left to proper quote investigators (and a timely one at that). Lehrer is alive though (unlike a certain someone...), so maybe one could even ask him?
Do you have a source questioning the authenticity? Not asking you to prove a negative here, just asking since I did not find one skimming a few pages on DuckDuckGo.
> The Onion: I'd long heard that you stopped performing as a form of protest, because Henry Kissinger won the Nobel Peace Prize.
> Tom Lehrer: I don't know how that got started. I've said that political satire became obsolete when Henry Kissinger was awarded the Nobel Prize. For one thing, I quit long before that happened, so historically it doesn't make any sense. I've heard that quoted back to me, but I've also heard it quoted that I was dead, so there you are. You can't believe anything you read. That was just an off-hand remark somebody picked up, and now it's been quoted and quoted, and therefore misquoted. I've heard that I stopped because Richard Nixon was elected, or because I got put away in an insane asylum, or whatever. It was just a remark about political satire, because it was true. Not literally, but everything is so weird in politics that it's very hard to be funny about it, I think. Years ago, it was much easier: We had Eisenhower to kick around. That was much funnier than Nixon.