Charlie Gibson Retires from ABC News; Diane Sawyer to Anchor 'World News'

Charles Gibson and Diane Sawyer co-anchor coverage of the Super Tuesday primaries, when 24 states headed to the polls to vote in the primary battle between then-Sens. Barack Obama and Hillary Clinton and in the Republican contest that would ultimately produce Sen. John McCain, R-Ariz., as the GOP nominee. (Ida Mae Astute/ABC)