Washington (CNN) Donald Trump's campaign still lacks a sufficient number of supportive delegates to guarantee that any revolt at the Republican National Convention could be put down, a key committee delegate says.

RNC Committeeman from Georgia and Rules Committee delegate Randy Evans, a lawyer who also works with the RNC and the Trump campaign, estimates that Trump has the support locked up of 888 delegates to Cleveland this month in the event of an effort to unbind delegates, leaving them free to vote for any candidate.

That's far short of the 1,237 -- a simple majority of total delegates -- that will be necessary to pass rules for the convention, leaving open the door for efforts to block Trump's nomination to continue. Evans' numbers were first reported by The Wall Street Journal

According to Evans' tally, 682 delegates are friendly to the delegate unbinding efforts. That leaves 903 potential swing votes.

Getting to a floor vote that allows delegates to vote for any candidate is still a long shot. The all-important Rules Committee creates a draft of the convention rules that will be voted on the floor. The panel has 112 delegates, but it only takes 28 to for what's called a minority report, even if the majority doesn't agree, that version of the rules also gets an up-or-down vote and debate on the floor.

Evans, with the help of Young Republican volunteers, has compiled a database of all the convention delegates using a combination of direct phone calls, scouring social media and combing through public affiliations. The effort was undertaken independent of the RNC and Trump campaign, Evans said, though he communicates with them. His priority is a "smooth convention," Evans added.

By Evans' estimate, there are currently only about 18 supportive members on the Rules Committee, with roughly 20 whose preference isn't known.

But Trump's camp pushed back on the numbers, saying that Evans' estimate vastly undervalued Trump's support in Cleveland.

"These numbers are completely ridiculous," a Trump adviser familiar with the campaign's whip operation said. "Mr. Trump will become the nominee at the convention and any conspiracy theory arguing otherwise is just plain silly."

One big wild card is Utah Sen. Mike Lee, who with his wife will serve on the Rules Committee. As one of the highest-profile members of the committee, who has not spoken publicly about his preferences but supported Texas Sen. Ted Cruz in the primary, Evans said Lee could sway a number of his colleagues.

"I think if Sen. Lee stands up in the Rules Committee and says, 'In the interest of transparency I think the delegates should get their choice,' I think they get their 28," Evans said.

Any effort to replace Trump as the nominee still is a long shot. But Evans notes that Trump's actions over the next few days will play a major role.

"So much depends on the dynamics of what happens between now and when the Rules Committee meets," Evans said. "If we have another Mexican judge tirade, I think that the numbers go up. If we have what we've seen for the last two weeks, then I think it's not very serious."

Lee's office said the senator remains undecided.

Still, struggles remain for unbinding

Still, the unbinding effort faces hurdles. Fracture lines have formed among the groups looking to unbind as crunch time nears.

Courageous Conservatives PAC and its main spokesman, Steve Lonegan, announced they would split from FreeTheDelegates as that group held a conference call Tuesday night with anti-Trump voices Bill Kristol and David French. The Weekly Standard editor and conservative lawyer and writer had in the past supported a third-party candidate to run against Trump.

Lonegan and CCPAC -- which had framed itself as the fundraising arm for FreeTheDelegates -- said talk of a non-GOP candidate crossed a line.

"My opinion is the support by this group of a third party undermines their credibility to be successful at the Rules Committee or anywhere else, and unfortunately it undermines our credibility as well," Lonegan said in an interview.

Lonegan, a New Jersey GOP strategist and former U.S. Senate candidate, said his group would still work to unbind delegates and "have the convention we should have," but added that "if Donald Trump's the nominee, so be it."

The lack of unity and a clear alternative to Trump makes things difficult to organize a successful anti-Trump movement. said Rules Committee member Solomon Yue of Oregon.

"(Mitt) Romney is a no, Paul Ryan, no -- so then you've got another problem: You are leaderless. And leaderless means candidate-less. You don't have a candidate you can all rally behind," Yue said. "When rebels split like this, they take down their own effectiveness to even organize seven states to raise an objection."

'It's on'

Kendal Unruh, the FreeTheDelegates leader, Colorado delegate and Rules Committee member, said she's undeterred and touted her group's new partnership with Delegates Unbound, an organization advocating allowing delegates to vote their conscience at the convention

In an interview, Unruh said that group "professionalizes" Free The Delegate's efforts, which had been volunteer-based.

Delegates Unbound, run by Republican strategists Dane Waters and Eric O'Keefe, has planned to put $2.5 million to $3.5 million into education, advertising, organizing and convention whip operations around unbinding delegates.

"This isn't going away no matter how anyone in the press or Donald Trump or the RNC try to mitigate it away -- it's on," Unruh said.

She said Kristol and French did not actually advocate for a third party. "Had he been on the phone call," Unruh said of Lonegan, "he would have heard that the Free The Delegates movement, and the fact that we can have a conscience convention, was something that backed (Kristol) away from that idea."

Kristol tweeted Wednesday that delegates should be free to vote their conscience, accusing the RNC of holding them back.

"Delegates are born free, but the RNC seeks to put them in chains," he tweeted , adding that he supports an uprising on the floor of the convention if those votes are not recognized. "I'm only for floor revolt if Chair fails to recognize right of delegates to demand roll call & record their votes."

I'm only for floor revolt if Chair fails to recognize right of delegates to demand roll call & record their votes.https://t.co/Jl9phS2udN — Bill Kristol (@BillKristol) July 6, 2016

Unruh has lowered expectations, telling the conference call and CNN that the goal is to get a minority report out of the Rules Committee, which requires one-quarter of the 112-delegate panel. That's down from her more bullish prediction of being able to sway a majority of the Rules Committee to adopt a rule that would unbind the delegates. The full convention must approve the rules at the beginning of proceedings in Cleveland.

Delegates may also simply take matters into their own hands, she said.

"It's looking more and more like it's going to boil down to the delegates realizing they are unbound without any codification and taking their innate right to be unbound to the floor and exercising it," Unruh said.

If the prior 2012 rules are passed without significant changes, as expected, the convention secretary would ignore those "conscience" votes and record the number of bound delegates for each candidate regardless.

It would take a majority of seven states' delegations to even raise a point of order to challenge that in the moment, Yue said.

Another rules long-timer, Bruce Ash of Arizona, poured cold water on the effort's chances.

"I think it just leaves Kendal and the rest of the group of dead-enders with one less friend," Ash said of the rift. "I think everybody understands that they lack the kind of support to pull off what they started out to do."