Are the tides in the late night wars turning? NBC, who has led in late night ratings since 1994, has just suffered its first November sweeps loss in 17 years, with David Letterman’s Late Show and Craig Ferguson’s Late Late Show beating both Jay Leno’s Tonight Show and Jimmy Fallon’s Late Night. Despite the very small margin of victory — Letterman averaged a 0.9 in the 18-49 demo vs. Leno’s 0.9 — this is pretty big news. Leno didn’t just eke out a win over Letterman for close to two decades, he completely decimated him for most of that, with Letterman routinely getting only 2/3 of Leno’s audience.

There are a lot of reasons for this, the chief of which is NBC’s completely pathetic ratings overall. Last night, literally twice as many people watched CBS’s primetime lineup (8 million) over NBC’s primetime lineup (4 million). And that’s by far their best night. And the real story here is probably the declining ratings of late night TV overall, which is frankly a dying format done in by oversaturation, declining ratings of all network TV and viewer disinterest.

But there’s no doubt now that the Conan/Leno debacle last year seriously damaged The Chin in the eyes of audiences. While his job is likely safe as long as he wants it (I doubt NBC will ever fire anyone ever again), The Tonight Show itself may not continue past him (and he’s 61 years old) if ratings and revenues continue to slide.