The Democratic National Committee and the news organization Politico are locked in an argument over the ideological credentials of a proposed moderator for next month's Democratic debate, sources familiar with the matter told NBC News. Politico and PBS are scheduled to co-host the sixth Democratic primary debate on Dec. 19 in Los Angeles. At the behest of its publisher, Robert Allbritton, Politico is pushing for Tim Alberta, the chief political correspondent for Politico Magazine, to join journalists from PBS Newshour at the moderators' desk. The top PBS journalists under consideration are Judy Woodruff, Yamiche Alcindor and Amna Nawaz. Politico’s decision...