Mike Wallace could be barred by his own network from covering gun-related stories on CBS News. The "60 Minutes" showboat correspondent appeared at a birthday party for columnist Art Buchwald -- a party that was also a fundraiser for the Brady Center, a prominent advocate of gun control laws. At the event Wallace showed a 47-second video of a past "60 Minutes" segment that, by Wallace's own admission, cast former NRA President Charlton Heston in a less-than-favorable light. In introducing the video, Wallace called Heston the "self-righteous enemy of the Sarah and Jim Brady bunch," according to a CBS News...