I was thinking this very thought just the other day, and just now I encountered it in this clever graphic, submitted by Peter W. to graphjam.com:
Those of a certain age will probably remember Vaughn Meader, who did an immensely popular imitation of JFK in the early 1960s. Meader’s career officially crashed on November 22, 1963. To be sure, Vaughn Meader was a one-trick pony, and Tina Fey isn’t. So her career will outlive Sarah Palin’s candidacy for Vice President. (Even if McCain-Palin were somehow to win, I suspect that Tina Fey would tire of doing the same thing over and over, and the joke would get pretty stale pretty soon anyway. So she’d go back the good career she’d been having before any of us had ever heard of Sarah Palin.) But Meader does provide an historical precedent for the point the graph is making.