CLEVELAND | From a spartan 16th floor office they've rented just blocks from this week's preliminary meetings of the Republican National Convention, some of the GOP rebels trying to head off Donald Trump are laying the groundwork for a revolt.

Dumping the party's presumptive presidential nominee is a longshot. They're up against an alliance between the Trump campaign and leaders of the Republican National Committee, which this week includes two dozen campaign operatives combing hotel lobbies and convention corridors counting votes and pressing delegates to oppose the dissidents.

Republicans say the Trump-RNC vote-counting "whip" team will swell to 150 when the Cleveland convention is in full swing next week.

Countering that, the renegade Republicans are setting up a high-tech messaging system to coordinate with organizers on the convention floor and plan to launch ads micro-targeted to the delegates' social media pages. They say they have organizers inside at least 35 state delegations who will help coordinate their drive to let the convention's 2,472 delegates vote for whichever candidate they want.

"There's so much energy to do this," said Dane Waters, co-founder of Delegates Unbound, one group challenging the widely held conventional wisdom that GOP rules require nearly all delegates to back a specific candidate, based on state primaries and caucuses. "Delegates are the authority of the Republican Party. This is about the future of the Republican Party."

Allied with other groups like Free the Delegates, they are facing a GOP establishment determined to prevent a toppling of the presumptive nominee - or any embarrassing, nationally televised showdowns during the four-day convention.

Underscoring that, the GOP rules committee - a bastion of establishment loyalists - on Tuesday formally proposed to renew rules that require delegates to back the candidate they are "bound" to. With no chance of prevailing at that meeting, the dissidents are saving their effort for later this week, when the separate convention rules committee meets to craft a rules package to be considered by the full convention next week.

"I highly doubt it," Republican National Committee Chairman Reince Priebus said in a brief interview of the prospects that the rebels would succeed. "I'm hearing less and less of it, actually. I think the unbind stuff has died off considerably over the last 10 days or so."

Others are more definitive. Randy Evans, a member of the RNC from Georgia, says Trump and party loyalist forces appear to have the convention "under control," with growing numbers of Republicans eager to avoid "the prospect of chaos" if the rules are abruptly changed.

Evans said Trump can apparently count on at least 1,700 devoted delegates - enough to fend off any rule changes. An Associated Press count shows that Trump has 1,543 delegates ready to back his nomination - more than the 1,273 he needs to officially clinch the top slot.

Dump Trump advocates say they have at least 400 delegate supporters but won't provide more detail. Even though Trump won more than 13 million votes and captured around 40 primaries and caucuses, his foes say he's not conservative enough and is likely to lose and drag down GOP congressional candidates with him.

"He's not a Republican, that's the problem," said Bill Eastland, a Trump delegate who like many of the dissidents, preferred Trump's former rival, Texas Sen. Ted Cruz.

Eastland says he supports the movement to allow delegates to back anyone, but concedes it will be "very, very difficult" to prevail. He says he fears blocking Trump "will actually do damage" to the GOP, in part because of how a spurned Trump might react to such a move.

Kendal Unruh, a Colorado delegate for Cruz and a leader of the "Dump Trump" effort, is pushing a proposal to let delegates vote their "conscience" by supporting the candidate of their choosing. She claims at least 28 members of the 112-member convention rules committee will support her - which if true would mean the full convention could vote on her proposal.

If she succeeds, top party and Trump campaign officials say her plan would be defeated.

"I'm sure she'd lose," said Steve Duprey, a Republican national committeeman from New Hampshire who's on both rules committees and is opposing the rebellion.

Unruh, Waters and their allies have other options. There's talk of other amendments proposing things like requiring the presidential candidate to release tax returns, and restricting future Republican primaries to only registered Republicans. Both proposed measures are aimed at Trump, who has not released his returns and won many independent votes in the Republican primaries.

The dissidents say they've enrolled parliamentarians and lawyers to help them demand roll call votes, recounts of how delegates are voting, and other steps that might turn the convention into an embarrassing, televised battle.

But such moves aren't easy. The convention's presiding officer - who at times will be Priebus or House Speaker Paul Ryan - has clout to decide who to recognize on the convention floor to make procedural motions.

In a show of party leaders' determination to keep things in hand, Duprey says, "It'll be a quick debate on the floor. We're not going to spend two hours debating rules."

If they do, said Unruh, "It will be on international TV that they ignored" the rebels and their interpretation of party rules.