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 to push for Alberta has rankled officials at the DNC, as well as some journalists at PBS and even Politico, the sources said. The reason: Alberta previously wrote for National Review, a conservative magazine, and has spent the bulk of his recent career chronicling the Republican Party.

Democratic Party officials say such a journalist is ill-suited to co-moderate a debate meant to better inform Democratic voters about their potential nominees.

In Politico’s eyes, Alberta is a nonpartisan journalist and shouldn’t be penalized because he covered the GOP or wrote for National Review. The news organization is continuing to push to have him on the panel.

Other Politico journalists who were under consideration for the co-moderator position were Carrie Budoff Brown, the site's editor, and Anna Palmer, the co-author of the influential Politico Playbook newsletter.

Representatives from both Politico and the DNC declined to comment. Alberta declined to comment.

The December debate will be the sixth and final debate of 2019, and could feature fewer candidates than in the prior debates because the DNC has stepped up the polling and fundraising thresholds for candidates to qualify.

To make the stage, candidates will need to hit 4 percent in at least four DNC-approved national or early voting state polls (up from 3 percent for the November debate), or alternatively, receive 6 percent or more support (up from 5 percent) in at least two approved early-state polls in Iowa, New Hampshire, South Carolina or Nevada.

Additionally, candidates also have to receive at least 200,000 unique donations (up from 165,000 for the November debate) and a minimum of 800 unique donors per state in at least 20 states.

Democratic National Committee Chair Tom Perez said in December 2018 that the party wanted to host 12 debates — six in 2019 and six in 2020, with the last in April.

The fifth Democratic debate, which is co-hosted by MSNBC and The Washington Post, is Wednesday in Atlanta. (NBCUniversal is the parent company of NBC News and MSNBC.)

The co-moderators for that debate are Rachel Maddow, host of MSNBC's "The Rachel Maddow Show"; Andrea Mitchell, host of MSNBC's "Andrea Mitchell Reports" and NBC News’ chief foreign affairs correspondent; Kristen Welker, NBC News White House correspondent; and Ashley Parker, a White House reporter for The Washington Post.

CORRECTION (Nov. 18, 2019, 6:20 p.m. ET): An earlier version of this article misstated Carrie Budoff Brown's position. She is the editor of Politico, but not the site's top editor.