But the DNC resisted the request in a statement shared with POLITICO: “The DNC has led a fair and transparent process and even told campaigns almost a year ago that the qualification criteria would go up later in the year — not one campaign objected. The DNC will not change the threshold for any one candidate and will not revert back to two consecutive nights with more than a dozen candidates. Our qualification criteria is extremely low and reflects where we are in the race. Once voting starts in February, our criteria will reflect those contests, which is more than appropriate. We’re proud to have given candidates so many opportunities to get their message across, and will continue to have fair criteria that reflects each point in the race.”

Another DNC official said that “multiple campaigns have privately signaled to the DNC their frustration with the large debate stage and asked them to hold the line.”

The Booker campaign was the driving force behind the effort to convince other campaigns to sign, according to several presidential campaign operatives familiar with the discussion.

The lobbying annoyed at least one other campaign that didn’t understand why they should help out a rival who had missed the clearly stated debate criteria.

"He prisoner‘s-dilemma’d us all into this as his campaign should be gracefully ending," a rival campaign operative said.

The letter made a plea for expanding the stage.

“Adopting the aforementioned criteria will produce a debate stage that better reflects our party and our country; will recognize a broader definition of what constitutes a viable candidacy, particularly in the early primary and caucus states where strong organization can outweigh media persuasion efforts; and will reflect the practical reality that the polling threshold has proven to be an unreliable metric, with only four national debate qualifying polls released since the last debate,” the letter reads in part. “With the holiday season upon us, and a brief qualification window for the January debate, it’s vital to make modifications to qualification criteria now.”

The possibility of candidates qualifying through an either/or pathway — instead of both requirements — would likely drastically increase the size of the stage, even if the thresholds are each increased individually.

If candidates could qualify for the December debate by hitting just one of the two thresholds, the seven candidates on stage would've been joined by Booker, Castro and Hawaii Rep. Tulsi Gabbard, who did not sign the letter.

An either/or pathway could also open up the possibility of former New York City Mayor Mike Bloomberg participating in the debates. Bloomberg has sworn off fundraising, closing the debate stage to him because he cannot hit any donor threshold. But a polls-only route could allow the billionaire, who has hit five percent in recent national qualifying polls, to participate.

It could even open the possibility for a candidate who has long been off the debate stage to return. Marianne Williamson, who has not participated since the first and second rounds of debate, did not publicly say she has hit the donor threshold for the December debate. But the spiritual guru has shown a proclivity for getting small-dollar support, having 140,000 donors at the end of the third quarter.

