WASHINGTON — The Democratic National Committee said on Monday that it would demand a slight increase in the polling and fund-raising thresholds that presidential candidates must meet in order to qualify for the party’s November primary debate, a move that may once again shrink the field of participating candidates.
To be invited to the November debate, candidates must have received donations from at least 165,000 individual donors and must meet one of two polling requirements. They must either receive 3 percent support in four national or early-state polls conducted by qualifying pollsters, or 5 percent support in two polls in the four early states: Iowa, New Hampshire, Nevada and South Carolina.
Polls will count if they were publicly released between Sept. 13 and midnight seven days before the debate. The date and location of the November debate have yet to be announced.
At least eight candidates have already met the 165,000-donor threshold, according to an analysis by The New York Times, though more candidates may have met it as well. Only three qualifying polls have been released since Sept. 13.
Candidates must also prove they have at least 600 unique donors in at least 20 states, United States territories or the District of Columbia, the D.N.C. said.
As the Democratic primary has progressed, party officials have gradually tightened the standards for debate qualification, making it harder and harder to clear the bar.
The 20 candidates who participated in the two-night debates held in June and July only had to amass donations from 65,000 people or reach 1 percent support in three qualifying polls. The qualification standards for this month’s debate were much stricter: Candidates were required to collect donations from 130,000 unique donors and achieve 2 percent support in four qualifying polls.
Only 10 candidates cleared the higher bar and the debate was held over just one night. With the addition of Tom Steyer, the former hedge fund investor, 11 candidates have already qualified for the October debate, which has the same requirements. Representative Tulsi Gabbard of Hawaii needs just one more qualifying poll result to make the cut.
The repeated tightening of the standards has caused considerable consternation among the candidates, causing many to gripe about the rules and nudging some to drop out of the race altogether. Aides to several of the second-tier candidates feared that Tom Perez, the D.N.C. chairman, would raise the bar much higher, effectively limiting the debate field to just a handful of candidates.
The modest threshold increase for the November debate came as a relief to on-the-bubble campaigns that had been preparing for a requirement of up to 260,000 individual donors, which would have forced unpleasant decisions about whether to divert resources from grass-roots organizing to online advertising in search of new donors.
Senator Kirsten Gillibrand of New York, Gov. Jay Inslee of Washington and John Hickenlooper, the former Colorado governor, exited the race in August after it became clear that they would not qualify for the fall debates. Mayor Bill de Blasio of New York dropped out last week after failing to qualify for the September debate and realizing he stood almost no chance of getting onstage next month.
Senator Amy Klobuchar of Minnesota and former Representative Beto O’Rourke of Texas, who both participated in the September debate and have qualified for the October one, have in recent weeks emailed appeals to supporters warning they could be left off the stage in November and December without an uptick in their fund-raising. Senator Cory Booker of New Jersey sent a message to supporters over the weekend, saying that without an infusion of $1.7 million by the end of the month his campaign may no longer be viable.
Gov. Steve Bullock of Montana, who did not qualify for the September debate and is not likely to make the stage for October’s, has been one of the most vocal critics of the process.
He renewed his attacks this month after it became clear that Mr. Steyer would qualify for the October debate after using millions of dollars of his own money to buy advertisements that have helped him draw in donations and increase his standing in the polls.
“At this point, there isn’t much left to be said regarding a set of rules that have allowed a billionaire to bankroll his way onto the debate stage, while governors and senators with decades of public service experience have been forced out of the race,” said Mr. Bullock, who has failed to earn 2 percent in a single qualifying poll. “This process is failing Democrats and does nothing to help us beat Donald Trump next November.”
The D.N.C.’s announcement may begin a new cycle of protests and recriminations from candidates who do not qualify. But while riding on a campaign bus in Iowa on Sunday, Mayor Pete Buttigieg of South Bend, Ind., who seems likely to make the November debate stage, was circumspect.
“I think it’s mission impossible for the D.N.C. to please everybody,” he said.
Maggie Astor contributed reporting.