The Republican National Committee's planned boycott of NBC and CNN over their dueling Hillary Clinton films got some liberal backing on Tuesday. David Brock, who founded the progressive Media Matters for America watchdog group, wrote to NBC today to throw his support behind RNC chariman Reince Priebus's criticism of the subject and timing of the two planned projects.

Why? Part of it, as evidenced by Priebus's threat itself, has to do with the talking point megaphone Media Matters believes a Clinton biopic would provide to conservatives on a potential candidate for 2016. Brock asks NBC if they're ready to answer three questions: 

Will you allow NBC News' name to be tarnished by NBC Entertainment's pursuit of ratings? 

Is you network also prepared to respond to criticism that it is not providing equal time to all political candidates? 

How will your network respond to the right-wing noise machine that is already pressuring you to adopt its ideological lens on Clinton? 

And, presuming that they are not able to adequately address those concerns, says that NBC should cancel their plans. Brock has a particular interest in protecting Clinton's messaging in the press, as Politico notes

Brock's motive is different from Priebus's, of course. In addition to heading MMFA, Brock is the chairman of American Bridge super PAC, which recently launched an effort called "Correct the Record" to protect Clinton and other Democrats from "Republican smears."

So in a way, Brock's move reads like more of a preemptive strike on what Democratic supporters are seeing as a conservative attack on Hillary Clinton's character. That campaign is already underway, even though Clinton hasn't even announced whether she's running or not. But there's another liberal objection to the films that's been picked up in some progressive circles, too: the fact that the RNC (or, for that matter, the DNC) has the leverage to threaten to end a lucrative partnership with the network over their content is problematic in the first place. John Nichols at the Nation focused in on that issue in a piece comparing news coverage of the Washington Post's sale to the RNC's intention to cut partnership ties with NBC and CNN for their party's primary debates: 

Network partnerships with the parties reinforce the worst status quo instincts—in our media and our politics. Americans should be interested in who owns newspapers, but they should be indignant about an arrangement that has television news operations negotiating with, partnering with and being threatened by political parties.

Priebus gave the networks until mid-August, when the RNC holds their summer meeting, to make a decision. Meanwhile, both networks have indicated that they'll go ahead with their plans. CNN is working on a feature-length documentary on Hillary Clinton, while NBC cast Diane Lane to play the former Secretary of State in a miniseries based on her life. There's also a third, widely-anticipated movie in the works from director James Ponsoldt

Here's the full letter from Media Matters: