In the latest round of musical chairs at the network news divisions, Martin Bashir is stepping down as one of the triumvirate anchors of ABC's Nightline and going solo in an afternoon slot at MSNBC and contributing to NBC's Dateline beginning in September. Bill Weir, who currently co-anchors the weekend edition of Good Morning America and contributes features to ABC's 20/20 news magazine, will replace Bashir. (MSNBC did not indicate whom Bashir will be replacing; ABC did not indicate who'll take over Weir's chores on GMA .) ABC used the occasion to taunt its rivals in the late-night competition. " Nightline has done what few imagined possible five years ago it has combined groundbreaking and important journalism with an appeal to the audience that has led it to grow while others in its time period have declined," ABC News chief David Westin said in a message to company employees. Separately, the network released new ratings comparisons noting that Nightline is currently tied with Late Show with David Letterman as the No. 2 late-night news show, The Tonight Show with Jay Leno holds a small lead over both.