The Colorado Republican Party came under siege Monday as presidential front-runner Donald Trump escalated his criticism of the state’s delegate selection process, calling it “a crooked deal.”

The billionaire businessman’s criticism came days after Sen. Ted Cruz captured all 34 Colorado national delegates at stake in a series of congressional district and state conventions.

“They are going absolutely crazy (in Colorado) because they weren’t given a vote,” Trump told the Fox News channel Monday, adding later “this was a political hack deal.”

Trump suggested Colorado GOP leaders canceled a binding presidential straw poll to “help a guy like Cruz” and accused his rival’s campaign of buying votes with favors.

“It’s not a system; there is no voting,” he said again and again in the interview, calling it “rigged.”

The remarks generated a frenzy of criticism across the nation about the Colorado caucus system and renewed questions about why the state didn’t hold a vote to allow broader participation.

The attention spotlighted party errors in the balloting that hurt the Trump campaign and raised questions about a possible challenge to the Colorado delegation at the Republican National Convention in Cleveland. A group that calls itself Colorado Votes Matter is organizing a protest Friday at GOP headquarters in Greenwood Village.

“The whole vote in Colorado should be thrown out because it was done badly,” said Shirley Robinson of Aurora, who volunteered Saturday at the state convention, where the final 13 delegates were decided.

Colorado Republican officials reaffirmed their decision not to hold a straw poll March 1 to make sure the state’s delegates were not bound to a candidate no longer in the race.

The caucus process this year is the same used in prior elections, where party members nominate delegates at the precinct level to higher levels, ultimately culminating in votes for national delegates at the congressional district and state conventions largely based on presidential preference.

Colorado GOP chairman Steve House pushed back against Trump’s attacks, saying 60,000 party members participated in the caucus and the party followed the rules.

“We ran a process exactly as the law prescribed, and this happens,” he said, acknowledging the errors but noting the efforts the party made to correct them at the convention. “I’m glad people are engaged, but a lot of this is over the top, for sure.”

The party’s critics posted House’s cellphone number online and asked people to call and express their displeasure. He said he received well over 2,000 calls since the results were announced.

The Cruz campaign, likewise, rejected the notion that it didn’t win the delegates fairly.

“We simply knew what the process was and followed it,” said Regina Thomson, a top Cruz organizer in Colorado. “They had as much opportunity to be engaged in this process as any other campaign.”

She also dismissed the idea that the rule change was made to benefit Cruz.

“It had nothing to do with a particular candidate because at that time there were 17 in the race,” Thomson said.

For the Trump campaign, the battle is expected to continue.

Of Cruz’s delegate haul, 30 are pledged to his campaign on the first ballot. The remaining four are unpledged delegates who announced their support for the Texas senator but technically remain free agents at what many expect will be a contested convention in July.

Patrick Davis, a Trump adviser in Colorado, told The Denver Post on Friday that the battle to win delegates didn’t end with the vote and he considers the unpledged delegates ripe territory for persuasion.

The Trump campaign put little effort into winning within the system, suggesting it was dominated by party insiders.

On the Cruz side, Thomson said she would get the unpledged supporters to sign legal affidavits requiring them to support Cruz, although the binding commitment is not effective until new paperwork is submitted on the floor at the national convention.

Most of the Cruz-pledged delegates declared they would support Cruz on every ballot, or at least until the candidate releases them.

Under Colorado Republican Party rules, the delegates who are pledged to Cruz cannot change their loyalties on the first ballot because they signed a document committing their vote, party officials said.

Asked in an interview Saturday with The Post what he will do to keep his Colorado delegates on additional ballots, Cruz sidestepped the question only to say the grass roots has been “our strength across the country from the beginning, and it is our overwhelming strength here in the state of Colorado.”

John Frank: 303-954-2409, jfrank@denverpost.com or @ByJohnFrank