Did Sarah Palin impression hurt Tina Fey's career?

Liberals praised her for mocking the 2008 GOP vice presidential nominee and Hollywood gave her an Emmy, but Tina Fey speculates in her new book, "Bossypants," that her impression of Sarah Palin cost NBC's 30 Rock some viewers:

"Some may argue that exploiting Governor Palin and her family helped bring attention to my low-rated TV show," Fey writes (via an excerpt in USA Today). "I am proud to say you are wrong. My TV show still enjoys very low ratings. In fact, I think the Palin stuff may have hurt the TV show. Let's face it, between Alec Baldwin and me there is a certain fifty percent of the population who think we are pinko Commie monsters."