"Apparently, when anyone votes against him, it's an act of theft," Cruz said on Beck's online radio show. He also told Beck the Trump campaign's "inability to even show up and win elections" makes it appear the front runner "can't run a lemonade stand."
"Donald, it ain't stealing when the voters vote against you -- it is the voters reclaiming this country and reclaiming sanity," Cruz told a San Diego crowd at a rally on Monday night.
In the last day, Cruz has hotly defended his campaign's efforts to send Cruz loyalists as delegates to this July's Republican National Convention in Cleveland.
Cruz's campaign swept up each of Colorado's 34 GOP delegates last weekend at its state and congressional district conventions after a similarly strong outcome in North Dakota the week prior. And in states that have already held their primaries or caucuses - like Tennessee, Arizona and Iowa - the Cruz campaign has effectively positioned its own supporters as Trump delegates in preparation for a second or third ballot that would allow them to vote for Cruz.
Trump tweeted bafflement on Sunday about the system: "I win a state in votes and then get non-representative delegates because they are offered all sorts of goodies by Cruz campaign. Bad system!"
On "Meet the Press" last Sunday,Trump's convention manager, Paul Manafort, correlated Cruz's campaign efforts to "Gestapo tactics."
Cruz credited his own supporters for turning out to the local conventions, where, most often, party activists select the national delegates.
"This is a matter of grassroots support showing up and activists showing up and voting and winning the election," Cruz said on the "John and Ken Show" on Los Angeles radio on Monday.
Trump countered on Monday at a rally in Albany, calling the Colorado system, which included seven congressional district conventions and a statewide convention, "a total fix," where the state took peoples' votes "and they gave it to these delegates."
Unlike Cruz, who spoke at the Colorado state convention, Trump did not make the trek to the West, and his campaign did not invest resources or strategy into delegate wrangling.
Trump's subsequent fiery condemnation of Colorado's Republican Party prompted U.S. Sen. Cory Gardner of Colorado to tweet on Monday night: "Elections are won by those who show up."
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And RNC Chair Reince Priebus tweeted "the rules have not changed" after Trump alleged the party switched from a traditional primary last year to hurt his candidacy.
"Now you may have noticed that when Donald loses, he gets very unhappy," Cruz told his roomful of San Diego supporters. "He yells and screams and stomps his foot. He curses and yells and insults anyone nearby. Look as we know in the state of California: 'Whine' is something best served with cheese."
Cruz is working to thwart controversy that he could win the nomination despite entering the convention with fewer delegates than Trump by asserting the nominee will be chosen by "delegates elected by the people."
But the delegate system is nuanced - in several states, traditional voters are far removed from the direct selection of the national delegates. In Colorado, Republican voters were invited to attend neighborhood caucuses on March 1 to select their congressional or county delegates, who then ultimately selected the state's national delegates last weekend.
In Tennessee, 14 at-large national delegates were chosen by the state GOP executive committee, which consists of members elected on Republican voters' primary ballots in 2014.