In yet another high-echelon shake-up at a network news division, CBS White House correspondent John Roberts, once regarded as a possible heir apparent to Dan Rather, announced Wednesday that he is joining CNN on February 20th. In a letter to colleagues, Roberts, who seemingly was passed over while the network focused all of its energy on attracting NBC's Katie Couric, expressed regret about leaving the CBS News "family" but gave no reason for his decision to do so. "Leaving CBS News will be difficult - no question. The ache of anxious anticipation has been gnawing away at me for some time now. It's not just the thought of leaving behind the comfort of familiar surroundings. It's about the many colleagues around the world whom I have come to call friends," he wrote. However, in an interview with USA Today, Roberts, who also anchors the Sunday edition of the CBS Evening News, said that when CBS News chief Sean McManus told journalists last month that no one at the network was being considered to anchor the CBS Evening News, he knew that his "options were going to be somewhat limited" at CBS. Separately, he told the Associated Press, "It became quite clear ... they were looking in a different direction for the main person other than me."