WASHINGTON (AFP) - US Republican presidential candidate Donald Trump alleged on Tuesday (May 3) that White House rival Ted Cruz's father was with John F. Kennedy's killer shortly before the US president was assassinated, prompting Mr Cruz to brand the Republican frontrunner a "pathological liar."
The startling allegation, and Mr Cruz's full-throated retort, occurred on the morning of a crucial primary election in Indiana where Mr Trump is seeking to land a knockout blow against his chief challenger for their party's nomination.
Mr Trump, parroting a recent story by the National Enquirer tabloid, took to Fox News to say the Texas senator's father Rafael Cruz, an immigrant from Cuba, was "with Lee Harvey Oswald" before the assassination.
"I mean, the whole thing is ridiculous. What is this? Right prior to his being shot, and nobody brings it up," Mr Trump told Fox by telephone.
"I mean, what was he doing - what was he doing with Lee Harvey Oswald shortly before the death - before the shooting? It's horrible."
The Enquirer, which has published previous stories deeply critical of Mr Cruz, said an Aug 16, 1963 photograph of Oswald in New Orleans handing out leaflets in support of Fidel Castro shows a young Rafael Cruz nearby.
Oswald was killed on Nov 24, 1963, two days after Kennedy's assassination.
Rafael Cruz was once a supporter of rebel leader Castro, but he admits in his biography A Time for Action that he was unaware that Castro was a communist, according to the Miami Herald.
The paper said there was no corroborating evidence that Mr Cruz - who is now fervently anti-communist - was affiliated with Oswald, and that the Cruz campaign said candidate's father is not in the photograph.
Trump's remarks incensed Mr Ted Cruz, who delivered a blistering takedown of the celebrity billionaire.
"Donald Trump alleges that my dad was involved in assassinating JFK," a visibly angry Mr Cruz told reporters at a campaign event in Indiana.
"Let's be clear, this is nuts," he said. "Yes, my dad killed JFK, he is secretly Elvis, and Jimmy Hoffa is buried in his backyard." Mr Cruz slammed Trump for several minutes unabated.
"This man is a pathological liar. He doesn't know the difference between truth and lies," Mr Cruz added, comparing Mr Trump to a schoolyard bully and saying the real estate mogul boasts of being a "serial philanderer."
"The man is utterly amoral," Mr Cruz said. "Bullies come from a deep, yawning cavern of insecurity."
Mr Cruz sees Indiana as one of the final firewalls where he could stop Mr Trump from seizing the Republican nomination.
"Indiana can pull us back, but it takes Hoosiers showing up and voting today, and the country is looking to Indiana, is looking to the judgment of the good men and women of this state," Mr Cruz insisted.
Mr Trump and Mr Cruz are battling it out for Indiana's 57 Republican delegates. If the billionaire sweeps them, he will be on track to reach the 1,237 necessary to win the nomination outright.