Update: AP reports Sunday night that Couric will leave CBS Nightly News prior to June 4.

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It wasn't supposed to be this way for CBS. Couric's good-natured cheer was as popular as Cheerios in the morning, resulting in demographic dominance for NBC's "Today Show."

With much fanfare, she broke into the old boys' club of network news anchors at a time when women were the majority of viewers. And unlike NBC, whose prime time had devolved from "Must See" to must-flee TV, CBS had the highest ratings.

But in part because she treated her opportunity as a "temp gig" and not a journalistic calling, Couric has been unable to pull CBS out of last place. According to Nielsen, the "CBS Evening News" averaged 6.43 million viewers during the first quarter of 2011 -- a two-decade low.