After the first two Democratic debates, Rep. Tim Ryan’s audiences grew from two or three people to 20. Former congressman John Delaney noticed an uptick in people approaching him in airports: “They grab my shoulder and say, ‘Hang in there. Your message is what we need to hear.’ ”

But now those low-polling candidates, and at least six others, are facing banishment from the prime-time glow of a national audience. The party’s rules for the next faceoff, on Sept. 12 and 13, will cut off any candidate who can’t score at least 2 percent in four approved polls and attract 130,000 donors.

That means the first real winnowing of this historically large field is at hand. About half the current candidates could be tossed off the debate stage and see their profiles sharply downgraded within days — a change likely to be cheered by many Democratic voters, who often say they find the sprawling field overwhelming.

It also presents those candidates with a tough choice as the Aug. 28 deadline to qualify approaches. Do they gracefully bow out of the presidential race, hoping to preserve goodwill and maybe a chance at higher office? Or do they become “zombie” candidates, staying alive long after the viability of their presidential dreams has ended?

That dilemma is prompting difficult conversations in many campaigns.

“The risk that all of these candidates have is continuing a presidential campaign that looks and feels like a fool’s errand,” said one adviser to a campaign, requesting anonymity to discuss internal deliberations. “They are at risk of doing damage to their credibility and their future ambitions.”

Three candidates, former Colorado governor John Hickenlooper, Washington Gov. Jay Inslee and Rep. Seth Moulton (D-Mass.) have already dropped out in recent days.

Some of the candidates are deeply frustrated by the Democratic Party rules forcing them off the debate stage, and they may voice their complaints at a Friday meeting of the Democratic National Committee in San Francisco.

Five men who appeared onstage in July — including the governor of Montana, the senior senator from Colorado and the mayor of New York City — have little hope of making the stage in September. Spiritual author Marianne Williamson is also likely to lose her spot.

Two others, Sen. Kirsten Gillibrand (D-N.Y.) and Rep. Tulsi Gabbard (D-Hawaii), still have a narrow chance of making the cut, along with newcomer Tom Steyer, a financier who has spent millions on television ads to juice his poll numbers.

The excluded candidates will have a shot of getting back on the big stage in October if they can meet the qualifications by then. But after that the road gets harder — DNC Chairman Tom Perez has made clear he intends to steadily raise the polling and donor thresholds for future debates.

Ten candidates have qualified for the September and October debates. If more make the grade in coming days, the debates will be split over two nights, according to host ABC News, with the candidates sorted by a random drawing.

Some Democrats fear that if numerous candidates hang on for months despite gaining little traction, it will be harder for the party to unify around a challenger to President Trump.

It would not be the first time presidential hopefuls have been slow to bow out of a primary — see former senator Rick Santorum (R-Pa.) in 2012 and former California governor Jerry Brown (D) in 1992. What’s different this time is the sheer number of Democratic candidates — currently 21 — including prominent figures who may be reluctant to exit.

The prospect of missing future debates helped prompt Hickenlooper and Inslee’s exits. Hickenlooper’s campaign began to rupture in June, when the debate rules were announced for September and October and some of his advisers concluded that his failure to qualify would be a prohibitive barrier to continued fundraising, according to people familiar with the discussions.

But for now, the remaining candidates facing demotion are promising to continue their campaigns undaunted. Some have focused their fire on the DNC’s rules, which they say allow those with deep pockets to buy their way onto the stage.

Montana Gov. Steve Bullock is especially critical of the way the DNC rules let someone such as Steyer, who is estimated to be worth $1.6 billion, spend his money to attract donors and run ads in hopes of driving up his poll numbers.

“The DNC donor requirements created a situation in which billionaires can buy their way onto the debate stage, and campaigns are forced to spend millions on digital ads chasing one dollar donors — not talking directly to voters,” he tweeted on Aug. 13.

The issue erupted into the open when Democratic Party leaders gathered in San Francisco for their summer meeting. Thirteen presidential candidates were scheduled to speak Friday, including six who have not qualified for the September debate.

“The DNC process is stifling debate at a time when we need it most,” Sen. Michael F. Bennet (D-Colo.), who will miss the September cutoff, said Friday when he addressed the body. “If we wanted to exclude people we would be Republicans.”

Craig Hughes, a senior Bennet adviser, said the debate rules were “developed in secret without consultation with state party chairs, activists or actual DNC members.”

He added: “A few operatives in Washington went into a backroom to put a thumb on the scale on behalf of perceived front-runners, celebrities and billionaires who can buy their way in. This is completely counterproductive to the interest of Democratic voters.”

Party officials say that they have been fully transparent about the debate rules and that it is reasonable to exclude candidates who cannot hit 2 percent in the polls or show grass-roots support after months of campaigning. Democratic leaders are sensitive to allegations that the 2016 nomination was rigged in favor of Hillary Clinton and say they are working hard to avoid an appearance that anyone was prematurely excluded.

Some candidates hope the fact that so many of them will be shut out will give rise to a sort of shadow campaign in which the left-out candidates can work together to raise their visibility. Thursday at the San Francisco party meeting, a proposal was made to encourage candidates to appear on the same stage and engage one another in multi-candidate forums. That proposal is part of a package that party members are scheduled to consider Saturday.

“There is going to be an interesting dynamic,” said Delaney, the former Maryland congressman. “Half are going to be on the debate stage, and half are not. There will be a lot of programming opportunities for the candidates who are not.”

Former congressman Joe Sestak (D-Pa.), who did not appear at the first debates and is unlikely to make the next one, has been vigorously campaigning in Iowa and New Hampshire nonetheless, in what may be a model for other candidates in the months to come.

Some candidates point out that the first debates did little to significantly change the polls; an initial spike in support for Sen. Kamala D. Harris (D-Calif.) after the first one appears to have faded. They also note that the first votes in Iowa and New Hampshire are still months away and that polls show that many voters have yet to make up their minds.

That means it is premature to keep anyone from the debates, they say. Even so, Ryan (D-Ohio), one of the few centrists in the race, said there is a lot of room to campaign even outside the debate hall.

“You are still going to be working the early states. You are going to be getting local TV in the early states,” he said. “And I think I have a pretty unique voice.’”

New York Mayor Bill de Blasio boasted last week of his recent appearances on two major television programs — the “Hannity” show on Fox News and “The Daily Show” on Comedy Central — with a combined audience he estimated at 5 million.

The Internet, too, gives candidates myriad ways to make contact with voters outside the party structure, from Instagram posts to digital ads.

“I think this is a wide-open situation,” de Blasio said. “There are going to be a lot more ways to spread the message.”

Yet already the landscape has been getting tougher for those outside the campaign’s top tier. Campaign advisers say it has been harder in recent weeks to book prime-time cable news spots for campaigns that are not registering in the polls.

In one sign of the shift, CNN has scheduled a town hall on climate change for Sept. 4 — but the network invited only candidates who have qualified for the September debate.

And the polls have become no kinder in recent weeks for those in the bottom of the pack. Gillibrand has committed more than $1 million — about 12 percent of her campaign chest as of the end of July — to television and digital ads in New Hampshire and Iowa in an effort to attract the 130,000 donors and 2 percent in polls that would qualify her for the debate. But Gillibrand has registered 2 percent in only a single poll, in early August in Iowa.

The senator from New York nonetheless remains upbeat about her prospects.

“We just had our first qualifying poll, and I expect to get the rest that I need in the next few weeks,” she said Monday in an appearance at a Washington Post Live event.

Delaney, who has spent two years campaigning with little impact on national or state polls, has hinted that he may begin airing ads after Labor Day in an effort to meet the polling threshold. A wealthy former businessman, Delaney has an outstanding loan to his campaign of about $15 million, according to Federal Election Commission filings. He spent less than $10 million through the end of June.

He suggested that if he misses the September debate, he could still hit his numbers in time for October.

“Not making the third debate but making the fourth isn’t actually a terrible story,” Delaney said. “You paddle to the next bend in the river.”