Brian Williams calls the evening news race “a back-and-forth dogfight.” But NBC may have more to worry about than the first place “World News with Charles Gibson.” The Nielsen numbers tell the story: in Katie Couric‘s first 39 weeks at CBS, she’s lost 287,000 viewers from the average of a year ago, a drop of 4 percent. At the same time, “Nightly News” lost 533,000 viewers, or 5 percent. TV consultant Andrew Tyndall tells the AP’s David Bauder: “if I was at NBC, I’d really be quite nervous about the hundreds of thousands of people that have left my audience.”