The Democratic National Committee is raising the bar when it comes to qualifying for next month’s presidential nomination debate, brushing aside an appeal spearheaded by Sen. Cory Booker of New Jersey to loosen the criteria as the new rules squeeze out middle-tier candidates from the stage.

The DNC on Friday announced even higher thresholds for the Jan.14 debate, which will be held at Drake University in Des Moines in the run-up to the Iowa caucuses.

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At Thursday’s debate in Los Angeles, just seven candidates qualified – excluding Booker - who failed to make the stage for the first time.

The onstage line-up represented roughly half of the remaining field of contenders. The DNC – which has been repeatedly criticized all year over their qualifying criteria – took heat for the lack of diversity at the Los Angeles debate, where the only non-white candidate was Andrew Yang, who is Asian-American.

Booker, who had urged the DNC to make the qualifications for next month’s debate more inclusive, reprised his criticism on Friday, telling reporters that the DNC’s “trying to dictate the choices to people here on the ground. It's really a shame when you talk to people ... on the ground. Most of them haven't made [up] their minds yet.”

Neither of the two remaining black candidates – Booker and former Massachusetts Gov. Deval Patrick – qualified for the last debate. And the field’s only Latino candidate, former Housing secretary and former San Antonio Mayor Julian Castro, also didn’t make the cut. Nor did Rep. Tulsi Gabbard of Hawaii, who’s Samoan-American.

In order to qualify for the next debate, candidates will need to reach one of two polling thresholds as well as a fundraising requirement. The White House hopefuls will have to hit at least 5 percent in four DNC-approved national or early-voting state (Iowa, New Hampshire, Nevada and South Carolina) polls – or reach at least 7 percent in two early-voting state surveys.

The fundraising criteria for the upcoming debate – which will be hosted by CNN and the Des Moines Register – requires campaign contributions from at least 225,000 individual donors as well as a minimum of 1,000 unique donors in at least 20 states.

Candidates have until the end of Jan. 10 to reach the thresholds, and the window for qualifying polling started on Nov. 14.

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Former Vice President Joe Biden; Sens. Bernie Sanders of Vermont, Elizabeth Warren of Massachusetts, and Amy Klobuchar of Minnesota; South Bend, Ind., Mayor Pete Buttigieg; billionaire environmental advocate and organizer Tom Steyer; and Yang qualified for the December debate. So did Sen. Kamala Harris of California, but she ended her White House bid ahead of the showdown.

Booker, Castro and Gabbard reported reaching the donor threshold but fell short of reaching the polling criteria.

On Saturday, Booker spearheaded a letter to the DNC asking the national party committee to "consider alternative debate qualification standards" for four nomination debates scheduled in January and February in the early voting states.

Booker argued that the higher thresholds have “unnecessarily and artificially narrowed what started as the strongest and most diverse Democratic field in history.”

Booker’s letter, which was co-signed by all seven candidates who were in the debate, as well as Castro, appeared to receive a frosty reception by the DNC.

Spokesperson Xochitl Hinojosa said in a statement in response to the letter that 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."

An optimistic Booker, on a campaign bus tour through Iowa, told reporters on Friday that “we are moving in the polls ... We would have been on that stage had there been more of an abundance of the polls in my opinion.”

And he downplayed the debates, saying “I don't think the debates are going to impact the year’s worth of work my campaign will have done.”

Booker also said that the “irony is you're gonna have a debate in Iowa, and all seven people who actually have real campaigns going on [in Iowa] are not necessarily going to be on that stage.”

Castro - who failed to qualify for the November and December debates - didn’t immediately react to the DNC’s new criteria. But in an email to supporters, his campaign made a fundraising pitch, writing that “the next debate thresholds have already been set, and we need a huge surge of support in order to get Julian on January’s stage.”

Patrick, speaking to Fox News on Thursday ahead of the DNC’s criteria news, said: “I hope they change in a way that is more inclusive.”

And he took aim at the debates, saying: “I hope, more than that, they change the format that it actually serves as a way to communicate with voters and not sort of as a cage fight among Democrats.”

On Friday, after the announcement, the Patrick campaign said “whether he's on or off the debate stage in January, our campaign is going to be working hard to ensure that every voter, everywhere, knows Deval's message and plan for renewing the American dream and why he's the only candidate in the race with the experience and record to bring this country together and win in November."