Donald Trump on Tuesday accused Ted Cruz’s dad of palling around with Lee Harvey Oswald just months before President Kennedy’s murder — prompting the Texas senator to fire back with his toughest attack yet on the Manhattan tycoon.

The GOP presidential front-runner, in a phone interview with Fox News, retold a National Enquirer story published last month that placed Rafael B. Cruz with Oswald, passing out pro-Fidel Castro literature in New Orleans on Aug. 16, 1963.

The supermarket tab ID’d the elder Cruz in a famous picture of Oswald and his communist-sympathizing buddies outside the International Trade Mart in New Orleans.

“His father was with Lee Harvey Oswald prior to Oswald’s being — you know, shot. I mean, the whole thing is ridiculous,” Trump said.

“What is this, right prior to his being shot, and nobody even brings it up. They don’t even talk about that. That was reported, and nobody talks about it.”

Trump stopped well short of accusing Cruz’s dad of plotting to kill JFK. But he still sought to place the elder Cruz alongside President Kennedy’s accused killer.

“I mean, what was he doing — what was he doing with Lee Harvey Oswald shortly before the death? Before the shooting?” Trump said. “It’s horrible.”

Cruz quickly responded by branding the ex-reality TV star a “pathological liar,”a “narcissist” and “immoral” on CNN.

“Donald Trump alleges that my dad was involved in assassinating JFK. Now, let’s be clear, this is nuts. This is just kooky. And while I’m at it I guess I should admit my dad killed JFK. He’s secretly really Elvis, and Jimmy Hoffa is buried in his backyard,” Cruz mocked before turning serious and unleashing a stunning barrage of personal insults.

“This man is a pathological liar. He doesn’t know the difference between truth and lies. He lies, practically every word that comes out of his mouth,” Cruz seethed. “The man is utterly a moron. Donald Trump is such a narcissist that President Obama looks at him and says, ‘Dude, what’s your problem?’”

Cruz, trailing badly in the polls and expected to lose Tuesday’s key Indiana primary, openly vented his frustration that Trump is winning despite his bullying and boorish treatment of women, including Cruz’s wife Heidi.

“Donald is terrified by strong women. He lashes out at them. Remember, this is the same Donald Trump who last week here in Indiana proudly touted the endorsement from Mike Tyson, a convicted rapist who served three years in prison here in Indiana for raping a 17-year-old girl and in Donald’s world, he said Mike Tyson was a tough guy,”Cruz fumed.

”I don’t think rapists are tough guys,” Cruz said, adding that Trump once went on Howard Stern’s radio show and compared “his battles with venereal disease as his own personal Vietnam.”

Oswald was arrested and accused of President Kennedy’s slaying on Nov. 22, 1963. He was murdered himself, two days later, by nightclub owner Jack Ruby.