Sen. Cory Booker Cory Anthony BookerSunday shows preview: Lawmakers prepare for SCOTUS confirmation hearings before election The movement to reform animal agriculture has reached a tipping point Watchdog confirms State Dept. canceled award for journalist who criticized Trump MORE (D-N.J.) led several of his fellow 2020 contenders in sending a petition asking the Democratic National Committee (DNC) to change its debate qualifications.

The New Jersey Democrat and eight other presidential candidates urged the DNC to "consider alternative debate qualification standards" for four primary debates scheduled to take place in January and Febraury in Iowa, New Hampshire, Nevada and South Carolina, which will host the first four nominating contests of the 2020 primary cycle.

Booker was joined by former Vice President Joe Biden Joe BidenBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Joe Biden should enact critical government reforms if he wins MORE, South Bend, Ind. Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE, former Housing and Urban Development Secretary Julian Castro Julian CastroSanders says Democrats should have given more speaking time to progressives Castro says DNC should have put more Latino speakers on stage from beginning Jill Biden defends husband's cognitive ability from Trump attacks: 'It's ridiculous' MORE, businessman Tom Steyer Tom SteyerTV ads favored Biden 2-1 in past month Inslee calls Biden climate plan 'perfect for the moment' OVERNIGHT ENERGY: Trump administration finalizes plan to open up Alaska wildlife refuge to drilling | California finalizes fuel efficiency deal with five automakers, undercutting Trump | Democrats use vulnerable GOP senators to get rare win on environment MORE, entrepreneur Andrew Yang Andrew YangBiden's latest small business outreach is just ... awful Doctor who allegedly assaulted Evelyn Yang arrested on federal charges The Hill's Campaign Report: Biden weighs in on police shootings | Who's moderating the debates | Trump trails in post-convention polls MORE and Sens. Amy Klobuchar Amy Klobuchar3 reasons why Biden is misreading the politics of court packing Social media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight MORE (D-Minn.), Bernie Sanders Bernie SandersTrump, Biden will not shake hands at first debate due to COVID-19 Sanders tells Maher 'there will be a number of plans' to remove Trump if he loses Sirota reacts to report of harassment, doxing by Harris supporters MORE (I-Vt.) and Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) in signing the petition.

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"The escalating thresholds over the past few months have unnecessarily and artificially narrowed what started as the strongest and most diverse Democratic field in history before voters have had a chance to be heard," the candidates said in the memo, which was obtained by The Hill.

"As a result, candidates who have proven both their viability and their commitment to the Democratic Party are being prematurely cut out of the nominating contest before many voters have even tuned in -- much less made their decision about whom to support."

Booker, who has languished in the low and middle tiers of the 2020 primary field and led the charge, failed to qualify for next week’s primary debate and has repeatedly pushed the DNC to ease its donor and polling thresholds.

To have qualified for the December debate, scheduled for Dec. 19, candidates had to amass the support of at least 200,000 unique donors and register at least 4 percent support in four qualifying polls or at least 6 percent support in two approved early voting state polls in Iowa, New Hampshire, Nevada or South Carolina.

The qualifications for December’s debate winnowed the field, with only Biden, Warren, Sanders, Buttigieg, Klobuchar, Steyer and Yang making the cut for the event, allowing for only one candidate of color. The field's diversity was further thrust into the spotlight after Sen. Kamala Harris Kamala HarrisPelosi: Trump Supreme Court pick 'threatens' Affordable Care Act What Kamala Harris' VP nomination means to us Harris slams Trump's Supreme Court pick as an attempt to 'destroy the Affordable Care Act' MORE, who is of Indian and Jamaican descent and the only other candidate of color to qualify for next week's stage, dropped out of the race.

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“While we know this was an unintended consequence of the DNC’s actions, many of the candidates excluded due to these thresholds are the ones who have helped make this year’s primary field historically diverse,” the candidates wrote in the memo.

“Frankly, that unintended result does not live up to the values of our Democratic Party and it does not serve the best interest of Democratic voters, who deserve to hear from and be able to choose among the best our party has to offer,” they added.

The contenders proposed in the memo that the DNC return to rules it applied to earlier debates that allowed candidates to qualify for the event via either the donor or the polling thresholds rather than both. Such a move could expand the debate stage back to a double-digit number of candidates and would include Booker and Castro, as well as former New York City Mayor Michael Bloomberg Michael BloombergBloomberg rolls out M ad buy to boost Biden in Florida Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Bloomberg pays fines for 32,000 felons in Florida so they can vote MORE and others.

"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 candidates wrote."

"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," they added. "If we are to beat Donald Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE next November, this must be our way forward."

The DNC defended its handling of the debates, maintaining that it has been transparent and made clear to all the candidates when the thresholds would be raised and by how much.

"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," the group said in a statement to The Hill

Updated at 9:02 p.m.