WASHINGTON — Struggling Democratic presidential candidates braced for bad news Wednesday with the window to qualify for the next debate set to close at midnight, a near impossible deadline for them to make and one that was likely to spell doom for their campaigns.
As time ticked down, New York Sen. Kirsten Gillibrand announced she was dropping out of the race after spending at least $4 million on advertising in recent months to qualify.
Billionaire climate change activist Tom Steyer, Montana Gov. Steve Bullock and self-help guru Marianne Williamson were also among those set to miss September’s debate, as were Colorado Sen. Michael Bennet, Hawaii Rep. Tulsi Gabbard and a handful of others.
To appear on stage in Houston next month, they have to hit 2% in at least four approved public opinion polls while securing 130,000 unique donors . Two new polls released Wednesday affirmed that they were all below the threshold.
With few developments expected before midnight, the question shifted from whether anyone else could qualify to whether anyone else would drop out.
‘‘Our rules have ended up less inclusive ... than even the Republicans,’’ Bullock said on MSNBC, referring to the thresholds set by the Democratic National Committee. ‘‘It is what it is.’’
In a still-crowded Democratic field, not qualifying for the debate would severely cripple the prospects of many candidacies, though several have pledged to forge on in hopes of reaching the requirements in time for the following debate in October.
Ten candidates have qualified for September’s debate: Joe Biden, Cory Booker, Pete Buttigieg, Julián Castro, Kamala Harris, Amy Klobuchar, Beto O’Rourke, Bernie Sanders, Elizabeth Warren and Andrew Yang.
Although earlier debates had lower thresholds, the DNC raised the stakes for the coming two.
‘‘We believe you need to show progress in your campaign,’’ said Democratic Party spokeswoman Xochitl Hinojosa. ‘‘There hasn’t been one candidate in 40 years who has polled under 2% the fall ahead of a primary and has gone on to be the Democratic nominee.’’
The DNC designed the requirements to bring order to an unwieldy field of more than 20 White House hopefuls, while elevating the role of online grassroots donors who are among the party’s most fervent supporters.
In some ways, the party has succeeded. But the process has drawn complaints from those unlikely to make the cut. They argue that the rules are arbitrary and have forced candidates to pour money into expensive online fundraising operations that can sometimes charge as much as $90 for every dollar raised.
Bennet said the threshold favored Steyer, and a memo by his campaign accused the billionaire of trying to buy his way into the debate. Steyer, a late entry to the race, is the closest to qualifying.
‘‘Other candidates have had to spend millions to acquire donors on Facebook, instead (of) communicating with voters and laying the groundwork to beat’’ President Donald Trump, the memo states.
A Steyer spokesman did not respond to a request for comment.
In a separate letter to Democratic Party Chairman Tom Perez, Bennet’s campaign asked how the DNC decided which polls to allow and questioned why Democrats were trying to narrow the field months before Iowa caucuses.
Yet Hinojosa, the DNC spokeswoman, said those who are upset have had ample time to build support and reach the thresholds.
Instead, most have consistently polled at 1% or below.
‘‘We are asking Democratic candidates to hit 2% in four polls. That is not a high threshold,’’ said Hinojosa, who added that the DNC is accepting the results from 21 polls.
Steyer and Gillibrand both poured millions of dollars into Facebook and TV ads to boost their standing in recent months. While Steyer met the donor threshold, he was still one poll shy. Gillibrand was three polls away and had yet to lock in enough donors.
Gabbard was two polls away from qualifying, and Williamson was three polls away.
Several others who struggled chose to drop out. Washington Gov. Jay Inlsee, Massachusetts Rep. Seth Moulton and former Colorado Gov. John Hickenlooper all recently ended their campaigns.
If the current roster of 10 qualifying candidates holds, the September debate would be the first of the cycle held on a single night. Earlier debates featured 20 candidates split across two nights.
Biden, the race’s early front-runner, said he would like the field to winnow even further.
‘‘I’m looking forward to getting to the place, assuming I’m still around, that it gets down to a smaller number of people so we can have more of a discussion instead of one-minute assertions,’’ the former vice president said Wednesday while campaigning in Spartanburg, South Carolina.
Associated Press writer Bill Barrow contributed to this report from Spartanburg, S.C.