Donald Trump has refused to promise to support the Republican candidate if he does not win the Republican nomination for the November election.
His rivals, Ted Cruz and John Kasic, declined to say whether they would unite behind the nominee.
All Republican candidates signed a pledge of allegiance last November.
This is the latest sign of friction between Donald Trump and Ted Cruz, who are involved in a dispute involving the other’s wives.
A commission supporting Ted Cruz posted a photo of Donald Trump’s wife Melania in 2000. In retaliation, Donald Trump posted an unpleasant photo of Ted Cruz’s wife Heidi on Twitter.
Asked by CNN about the dispute, Donald Trump told Ted Cruz: “He started it.”
CNN presenter Anderson Cooper answered and said: “But, sir, with all due respect, that’s the argument of a five-year-old.”
“No it is not,” said Donald Trump.
Donald Trump claims that he was treated very unfairly in the campaign.
Asked if he had kept his promise of loyalty from last November, Donald Trump said: “No, I don’t do it anymore.”
Earlier, when the same question was asked, Ted Cruz did not give a direct answer, but said: “I’m not in the habit of supporting someone who attacks my wife and attacks my family.”
He continued: “Donald will not be nominated for the GOP. We will defeat him. ”
Donald Trump later responded by saying he did not need Ted Cruz’s support: “I have a lot of support from the people right now.”
The New York tycoon has been repeatedly criticized by his rivals and observers for a campaign that includes personal attacks on rivals and criticism and violence against protesters.
Despite the many recent controversies surrounding him, Donald Trump is currently well ahead in the Republican race with 739 delegates out of 465 at Ted Cruz.
John Kasic is 143 behind, with the 1,237 needed to win the nomination probably out of his reach.
The three candidates campaigned in Wisconsin before the primary on April 5.