• In a leaked video, Republican presidential nominee Donald Trump repeated false conspiracy theories about childhood vaccinations on a call with third-party presidential candidate Robert F. Kennedy, Jr.
• The clip also shows Trump telling his ostensible campaign rival, "I would love you to do something."
• The call allegedly took place one day after Trump survived an assassination attempt at a campaign rally in Pennsylvania on Saturday. The video clip does not appear to show the entire call.

Republican presidential nominee Donald Trump repeated false conspiracy theories about childhood vaccinations during a recent call with the third-party presidential candidate Robert F. Kennedy Jr., according to a video of the call leaked Tuesday.

Trump can be heard saying that, after receiving vaccines to protect infants against life-threatening diseases, "You see the baby all of a sudden starting to change radically."

The clip also shows Trump telling his ostensible campaign rival, "I would love you to do something. And I think it'll be so good for you and so big for you."

When Trump adds, "We're going to win" the election, Kennedy responds, "Yeah."

It was not clear what Trump was suggesting Kennedy should do. A Trump campaign spokesman did not immediately respond to CNBC's request for clarification about the leaked conversation, which Kennedy verified later Tuesday morning.

But the clip offers more evidence for Biden supporters who have accused Kennedy of running a spoiler campaign that is likely to benefit Trump in November.

The 98-second video, which was posted online and then deleted by Kennedy's son, Bobby Kennedy III, captures Trump's voice on a cell phone being held by Kennedy, an independent presidential candidate and documented vaccine conspiracist and distributor of vaccine disinformation.

"I agree with you," Trump is heard saying at the start of the clip. "Something's wrong with that whole system."

"Remember how I said, 'I want to do small doses, small doses.' When you, when you feed a baby, Bobby, in vaccination, that it's like 38 different vaccines and it looks like it's meant for a horse," Trump says.

"Not a 10 pound or 20 pound baby. It looks like you're giving, you should be giving a horse this. And you ever see the size of it, right? There's this massive, and then you see the baby all of a sudden starting to change radically. I've seen it too many times and then you hear it doesn't have an impact, right?" Trump says.

"There's this massive, and then you see the baby all of a sudden starting to change radically," Trump claims. "I've seen it too many times and then you hear it doesn't have an impact, right?"

Unfounded skepticism and online disinformation about the safety of childhood vaccinations has caused childhood vaccination levels in the United States to fall in recent years, a trend that was exacerbated by the COVID-19 pandemic.

Kennedy III said the call took place one day after Trump survived an assassination attempt at a campaign rally in Pennsylvania on Saturday. The video clip does not appear to show the entire call.

Trump told Kennedy that President Joe Biden was "very nice" when he called after the shooting, in which Trump sustained a minor injury and one rallygoer was killed.

The bullet that whizzed by his head sounded "like the world's largest mosquito," Trump told Kennedy.

Kennedy, in a post on X later Tuesday morning, apologized to Trump for the leak, saying he was "mortified that this was posted."

"When President Trump called me I was taping with an in-house videographer," Kennedy wrote.

"I should have ordered the videographer to stop recording immediately," he said. "I apologize to the president."

Kennedy III had initially posted the video in an X post, writing, "I am a firm believer that these sorts of conversations should be had in public."

"Here's Trump giving his real opinion to my dad about vaccinating kids," the younger Kennedy wrote, adding, "This is not a cheapfake or somebody doing a Trump voice. This is the real deal."

Kennedy III's post went on criticize Trump's choice of running mate, Sen. JD Vance of Ohio, and accused him of holding pro-vaccine views.

After deleting that post, Kennedy tweeted that he had been wrong about Vance. "Removed last one for mistaking sarcasm for real life," he wrote.

Trump and Kennedy met in person on Monday in Milwaukee, where the Republican National Convention is underway.

The Biden campaign pounced on the leak, saying in a press release, "it makes sense that Trump would find common cause with anti-vax extremist RFK Jr."

"Trump and his anti-vax bud 'Bobby' are spreading dangerous conspiracy theories that threaten the lifesaving care that tens of millions of people depend on," Biden campaign spokesman Joe Costello said in the release.