Campaign buttons of declared and undeclared Republican presidential candidates are arranged at the Iowa Faith & Freedom Coalition presidential forum on April 25 in Waukee, Iowa. (Daniel Acker/Bloomberg)

A pivotal turning point in the Republican presidential race will come in August, when the first debate of the primary season is held in Cleveland.

But there’s already a problem: Not everyone will make it on stage.

There could be 16 or more declared candidates by then in one of the most robust GOP presidential fields in history. Another half-dozen are contemplating long-shot bids.

No GOP primary debate has ever included more than 10 candidates. Even if this year’s stage is more crowded than in the past, some reasonably serious White House aspirants are bound to be left out.

The criteria for who will qualify to participate will be set by the news organization producing each debate, with input from party officials. This year, the behind-the-scenes discussions have been the source of acute angst at the Republican National Committee, which has floated using factors such as campaign donations and early-state staffing to winnow the pool, according to people familiar with the discussions.

The party streamlined the debate schedule this year to avoid the nonstop televised showdowns that stretched through the 2012 primaries, which RNC Chairman Reince Priebus dubbed “an embarrassment.” This time, the RNC has sanctioned up to 12 debates, down from 20 four years ago.

But figuring out who can take part in the forums has been a thornier problem. Cutting out lower-ranked aspirants such as former Hewlett-Packard chief executive Carly Fiorina and Louisiana Gov. Bobby Jindal would make the first debate of the 2016 season a tableau of men, most of them white — not the image the party wants to promote as it faces an increasingly diverse electorate.

RNC Communications Director Sean Spicer said the party’s aim is to provide candidates with clear guidelines early in the process.

“While the networks ultimately will establish the criteria, our goal is to make sure that the criteria to get in the debate is known as soon as possible,” he said.

Fox News and CNN, which host the first two debates, declined to comment on what thresholds they will use.

In past years, Fox News determined debate qualification in part by looking at the top 10 candidates who had hit at least 1 percent in the five most recent national polls. As of now, 15 of the top 16 potential candidates have at least 1 percent, according to an average of the five most recent phone surveys testing support for the GOP nomination.

The top 10 candidates on that basis are former Florida governor Jeb Bush, Sen. Marco Rubio of Florida, Wisconsin Gov. Scott Walker, Sen. Rand Paul of Kentucky, Sen. Ted Cruz of Texas, former Arkansas governor Mike Huckabee, real estate tycoon Donald Trump, retired neurosurgeon Ben Carson, New Jersey Gov. Chris Christie and former Texas governor Rick Perry.

Lagging behind Perry with less than 2 percent are former senator Rick Santorum of Pennsylvania, Ohio Gov. John Kasich, Sen. Lindsey O. Graham of South Carolina, Jindal and Fiorina. Former New York governor George Pataki averages a mere half-point.

All are sure to balk if they are excluded.

“As Republicans, we should seek ways to get more exposure to more of our leaders,” said Curt Anderson, a Jindal strategist. He added that the Louisiana governor does not plan to announce his plans until after the state’s legislative session ends in June, “so there is no possibility of him registering much in the polls until later this year.”

The first debate, hosted by Fox News, is slated to be held Aug. 6, according to the Northeast Ohio Media Group. The second forum, to be held at the Reagan Library in Simi Valley, Calif., on Sept. 16, will be carried by CNN. The third will take place in Colorado in October and air on CNBC.

Among the novel ideas that have been floated to determine a candidate’s strength is the amount of money raised by his or her campaign committee, according to people with knowledge of the talks. But many candidates will not file an initial fundraising report until mid-October. So what about money raised to support them through independent super PACs, which this year are largely functioning as extensions of the official campaigns? (That concept has gotten little traction.)

Other possible criteria are rankings in state polls and the number of staff on the ground in the early nominating states.

“It is that complicated,” said one person familiar with the discussions. “Every time you think you’ve come up with a fair and equitable way, there’s a reason why that scenario falls apart.”

The only guarantee for now, it appears, is that early GOP debates will be colorful and crowded affairs.

“Don’t forget, I have done a lot of live television,” Trump said in an interview, referring to his long run as host of NBC’s “The Celebrity Apprentice.” “The people I dealt with on live television — I think, in many cases, they’re smarter than the people we’re talking about.”

Scott Clement contributed to this report.