The fallout from CBS's doomed story about President Bush's National Guard service most endangers a woman few viewers know but who played a key role in two of the biggest television stories of the year. Mary Mapes, a veteran producer at CBS News, reported most of the National Guard story, including obtaining the documents CBS now says it can't authenticate. She also passed on the phone number of her source, former Texas National Guard officer Bill Burkett, to the Kerry campaign. ... CBS acknowledged Mapes passed on Burkett's number to Kerry adviser Joe Lockhart, and Lockhart called him. Spokeswoman Kelli...