DES MOINES, Iowa — Donald Trump’s relentless assault on the rules that govern how Republicans choose their nominee is coming far too late to change what even defenders acknowledge is a complicated selection system.

He seems to know it, too.

Instead, his railing against a “rigged” process appears aimed at amplifying his central message to an angry electorate: America is a mess, and only Trump can clean it up.

In the Wall Street Journal on Friday, he equated the party’s nomination procedures with the “unfair trade, immigration and economic policies that have also been rigged against Americans.”

He added, “Let me ask America a question: How has the ‘system’ been working out for you and your family?

Underlying the constant criticism, Trump’s goal is to rally supporters and pile up primary season victories that would bring him the 1,237 delegates needed to win the nomination outright before the summer convention. But it’s a tactic that Republicans say carries real risks for the billionaire businessman.

Should Trump fall short of that clinching number going into the Cleveland convention in July, his rantings against the party are likely to annoy the delegates who would then decide the nominee, they said.

“He is trying to pit voters against the very people who make the decision of whether he gets the nomination,” said Matt Borges, chairman of the Republican Party in Ohio. “If he does not arrive in Cleveland with 1,237 pledged delegates, then there is no way he gets the nomination.”

Trump says he has all the tools he needs to assuage any annoyed delegates.

“Nobody has better toys than I do,” Trump told attendees Sunday at a Staten Island GOP county brunch.

“I can fly [delegates] on the best planes and take them to the best resorts around,” including his private club in Florida, Mar-a-Lago. “You’re basically buying these people. You’re basically saying, ‘Delegates, listen we’re going to send you to Mar-a-Lago on a Boeing 757, you’re going to use the spa, you’re going to this, you’re going to that.’ That’s a corrupt system. That’s not a democracy.”

Trump’s tirades have aired the backroom tension with the party. But GOP officials are pushing against the front-runner’s accusations of unfairness.

Republican National Committee Chairman Reince Preibus took to Trump’s favorite medium, Twitter, to make the point that the nomination process has been known to all for more than a year.

“It’s the responsibility of the campaigns to understand it,” Priebus wrote. “Complaints now? Give us all a break.”

Priebus told NBC’s “Meet the Press” on Sunday that he will not allow Trump to bully him, and noted that a majority — not a plurality — rules in most aspects of governance. “The rules are set. . . . I’m not going to allow anyone to rewrite rules for the party.”

On Friday, the party’s chief strategist, Sean Spicer, laid out the rules for elected delegates in each of the remaining states that will hold primary contests.

Spicer noted those rules were shared with all the campaigns last year, adding that “each process is easy to understand for those willing to learn it.”

At the same time, however, party insiders who make the rules appear keenly aware of the emotions that Trump is stirring.

At a rally last week in New York, Trump said RNC members “should be ashamed of themselves for allowing this crap.”

Several of those involved in the rule-making process told The Associated Press that they believe there’s a consensus inside the party against considering changes before the convention.

“We want to avoid even the appearance that somehow, the RNC is trying to meddle or manipulate the convention process,” Florida GOP committeeman Peter Feaman said.

That isn’t likely to do much to placate Trump. He says the process should favor the candidate who wins the most votes during the primary campaign.

Trump has received about 8.2 million votes to date, about 2 million more than his closest competitor, Texas Sen. Ted Cruz.

Cruz is outmaneuvering Trump in lining up support among the individuals who will attend the Cleveland convention as delegates. That’s a separate process, in which party activists seek the positions primarily through local, district and state party conventions.

If Trump can’t clinch by the time the last group of primaries, on June 7, then those delegates will largely be free after the first ballot at the convention to vote for the candidate of their choice.

“To be fair, it’s complicated for everyone,” said Ron Kaufman, a longtime member of the RNC’s standing rules committee. “And I understand why someone who’s never done it before, and hasn’t taken time to learn it, gets frustrated.”

But that frustration isn’t winning Trump any friends among the party officials who will have sway at a multi-ballot convention.

Henry Barbour, also a rules committee member, put it more simply: Trump’s attack on the party and the delegate selection process is bad politics.

“If you want to ask a girl to the prom, you don’t tell her how ugly she is the week before,” Barbour said.

Associated Press writers Jonathan Lemire in Staten Island, N.Y., Alan Fram in Washington and Bill Barrow in Atlanta contributed to this report.