From the December 26, 2004, interview (with Brian Lamb):
WILLIAMS: I do listen to Rush. I listen to it from a radio in my office, or depending on my day, if I'm in the car, I will listen to Rush. And he will tell you I've been listening for years. I think it's my duty to listen to Rush. I think Rush has actually yet to get the credit he is due, because his audience for so many years felt they were in the wilderness of this country. No one was talking to them.
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Rush said to millions of Americans, you have a home. Come with me. For three hours a day you can listen and hear the like-minded calling in from across the country, and I'll read to you things perhaps you didn't see that are out there. I think Rush gave birth to the FOX News Channel. I think Rush helped to give birth to a movement. I think he played his part in the Contract with America. So I hope he gets his due as a broadcaster.
For more:
http://mediamatters.org/items/200501240007