Tensions between the Republican Party and its own front-runner erupted into a full-blown public battle as top party officials rebuked Donald Trump on Friday for alleging that the GOP primary system was “rigged” against him.

The dispute, which has been simmering for days, centers on Trump’s failure to win any delegates last weekend in Colorado, which selected its 34 delegates at a party convention rather than a primary attended by voters. All went to Trump’s chief rival, Sen. Ted Cruz of Texas.

The outcome prompted a daily stream of complaints and allegations this week from Trump, who wrote in an op-ed published in Friday’s Wall Street Journal that the “system is being rigged by party operatives with ‘double-agent’ delegates who reject the decisions of voters.”