Headlined “Let me ask America a question,” Trump wrote, “How has the ‘system’ been working out for you and your family?”

Trump condemned Colorado’s delegate selection process as undemocratic. “One million Republicans in Colorado were sidelined,” he wrote, challenging Americans to judge the current “system.”

“I, for one, am not interested in defending a system that for decades has served the interest of political parties at the expense of the people,” the Republican front-runner declared. “No one forced anyone to cancel the vote in Colorado. Political insiders made a choice to cancel it. And it was the wrong choice.”

The Republican Party in Colorado last year decided to forgo holding an open presidential primary or caucus contest for the 2016 cycle due to cost concerns, choosing instead to have party members select delegates at the state convention.

But Republican National Committee Chairman Reince Priebus defended the nominating process Friday in an interview with CNN’s Wolf Blitzer, saying that if Trump doesn’t like the rules, he can change them.

“This is a very normal system that we’ve been using many for years,” Priebus said on “Wolf.” “And by the way, if anyone wants to reform the system, they can do so on the Rules Committee, because every four years, the Rules Committee gets together and they write the rules for the nomination of our party. So that’s who writes the rules. It’s not the RNC that writes the rules to determine the system.”

Also on Friday, Sean Spicer, the RNC communications director, reiterated that “the rules surrounding the delegate selection have been clearly laid out” for months, and noted that delegates can be awarded “through a primary, caucus, or convention” — the last being the particular target of Trump’s frustration.

But despite Trump’s charge in his piece that “what we are seeing now is not a proper use of the rules, but a flagrant abuse of the rules,” the RNC adamantly resisted those claims. “The RNC is transparent about the rules and works with campaigns on a consistent basis to address any questions surrounding the process,” Spicer wrote in Friday’s memo.

Seeming to respond indirectly to Trump, he also wrote, “it ultimately falls on the campaigns to be up to speed on these delegate rules.”

“Each process is easy to understand for those willing to learn it.”

Trump sought to link primary rival Texas Sen. Ted Cruz to those insiders seeking to deny him the nomination. “The great irony of this campaign is that the ‘Washington cartel’ that Mr. Cruz rails against is the very group he is relying upon in his voter-nullification scheme,” he wrote.

“My campaign strategy is to win with the voters,” Trump added. “Ted Cruz’s campaign strategy is to win despite them.”