“It’s offensive and it speaks to a lack of knowledge about this process. I think everyone needs to go back and take civics lesson again,” added a member of the Republican National Committee who requested anonymity in order to speak candidly because this individual will be serving as a convention delegate in Cleveland this July.

Hundreds of party insiders, including around 170 RNC members who are automatic convention delegates, gathered this week at an upscale oceanfront resort in south Florida to prepare for a possible contested convention. They were also were attending private briefings conducted by the campaigns of Trump, Sen. Ted Cruz of Texas and Ohio Gov. John Kasich designed to build support, and win votes, in the event of a multi-ballot floor fight.

Illustrating just how important these delegates have become, Cruz and Kasich diverted from the campaign trail on Wednesday to woo them, travling to the RNC’s regularly scheduled spring meeting, at the Diplomat Resort and Spa in Hollywood, Fla., near Ft. Lauderdale. This was despite the fact there are primaries scheduled in five states in less than a week that present critical opportunities for them to try to accumulate more delegates and narrow their gap with Trump.

Delegates could have enormous power at a contested convention. The delegate pool is comprised of RNC members, plus more than 2,000 others, including alternate delegates, that are going through the election and selection process in states across the country. These activists often comprise the bulwark of the volunteer ground forces presidential campaigns need to help them get the out the vote and win in key battlegrounds.

So it was hardly by accident that Cruz defended their integrity against Trump’s charges that they are on the take and participating in a system that is un-democratic. The senator had concluded a news conference here Wednesday afternoon but stopped half way out the door of a hotel conference room here to make this point when asked if his meeting with RNC members constituted colluding with the GOP establishment.

“The strength of our campaign and the strength of our party is the grassroots,” Cruz said. “And, it is not beneficial for the party or for the country to have a presidential candidate that looks down on the grassroots. I am happy to go where the grassroots are, to ask for their supports and to answer their questions at any and all times.”

Trump has won the bulk of the primary and caucus elections held so far, and won more support from voters in these contests than Cruz or Kasich.

That has allowed him to rack up more delegates bound to vote for him on the first ballot at the convention — and in some cases second and third ballots — than either of his competitors. Indeed, only Trump can clinch the nomination in the remaining primaries; Cruz and Kasich can only win it by a vote of the delegates in Cleveland. Trump leads in delegates 845 to 559 for Cruz, with Kasich trailing at 148.

But Trump has taken a beating in the county, district and state elections that act as the selection mechanisms for the individuals who serve as delegates (so has Kasich.) Cruz’s superior grassroots operation, fielded months ago, has been installing loyalists in convention delegations that are prepared to vote for him once they are unbound from the candidate that won their state’s primary or caucus and become free agents.

Cruz’s success has extended to states like Arizona and Georgia, where Trump won the voter preference primary quite easily. Trump has responded by blaming an unjust system for his campaign’s delegate failures, saying it disenfranchises voters. “It’s a crooked system, it’s a system that’s rigged and we’re going to go back to the old way, it’s called you vote and you win,” he said Tuesday night after his landslide victory in New York.

Trump has vowed to overhaul GOP rules if he is elected president and becomes head of the party.

Veteran Republicans say they understand the politics behind Trump attacking their party’s processes. There hasn’t been a contested GOP convention in 40 years, most voters are unfamiliar with the role of delegates in the nomination. And, at time when anti-establishment fervor is running high, Trump could win votes with his attack on national party.

But RNC members say Trump is carrying his criticism too far — to his detriment.

To begin with, there is little appetite among GOP activists to create uniform rules for presidential nominations. The state parties are jealous of their power to make their own rules, and compared it to the conservative, Republican principle of limited government and valuing states’ rights.

Additionally, while they can understand generalized attacks on the system for political gain, Trump essentially calling them all crooks, and referring an organization they have in some cases devoted years of their life to as corrupt, is too much for them to stomach. Trump could end up regretting his rhetoric, they said, especially if Cleveland, or November, doesn’t go his way.

“I understand the public relations value of the candidate saying, you know the system’s rigged, but it isn’t. All they had to do is read the rules, and you know in Donald Trump’s book, ‘The Art of the Deal,’ he says be prepared,” Steve Duprey, the RNC committeeman and delegate from New Hampshire, said.