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.

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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. On Monday, he sent another email acknowledging the newly released debate thresholds, noting that he had not reached 165,000 individual donors and asking supporters to chip in. According to the Times analysis, he is the only candidate who has participated in all of the debates and has not yet reached 165,000 donors.