US presidential primaries: Ted Cruz accuses Donald Trump of threatening delegates

Trump on the other hand has continued to rail against a nominating system he says is crooked and rigged

Texas Sen Ted Cruz blasted rival Donald Trump in a radio interview, accusing the Republican front-runner of being a bully, inciting violence and using dirty tricks to intimidate voters and delegates, as Trump continued to rail against a nominating system he says is crooked and rigged.

Using some of the harshest rhetoric of the campaign to date, Cruz said his billionaire rival is a bad businessman who has been surrounded by sycophants his entire career.

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"Donald's whole pitch is he's a great businessman," Cruz said in a wide-ranging interview on the Glenn Beck radio show, adding that given how Trump runs his campaign, "it appears he can't run a lemonade stand."

The comments came as both campaigns work tirelessly behind the scenes to secure delegates who will back them at the Republican Party convention this summer in Cleveland.

So far, Trump has appeared badly outmaneuvered by a better-organized Cruz operation, prompting the real estate mogul to rail against the Republican electoral system, claiming that the will of the voters is being denied.

"Our Republican system is absolutely rigged. It's a phony deal," said Trump at a rally in a packed airport hangar in Rome, New York, on Tuesday evening, where his speech was dominated by foot-stomping over the primary process.

He pointed to Colorado, where he said the delegate-selection system was set up by "crooked politicians" to make sure an outsider like him could never win.

"These are dirty tricksters," he said, placing the blame on the Republican National Committee. "They should be ashamed of themselves for allowing this kind of crap to happen," he added, saying that both Republicans and Democrats have set up "phony rules and regulations" that makes it "impossible for a guy that wins to win."

He went further a few hours later during a CNN town hall in New York City, suggesting the RNC was actively working to defeat him.

"The RNC doesn't like this happening. They don't like that I'm putting up my own money because it means they don't have any control over me," Trump said, arguing that the deck is "stacked against me by the establishment".