Trump says RFK Jr. will hurt Biden. In private, he's not so sure.

Former President Donald Trump has repeatedly said he’s confident that independent presidential candidate Robert F. Kennedy Jr. will pull more votes away from President Joe Biden than from him — a net win for the Republican’s candidacy.

“He is Crooked Joe Biden’s Political Opponent, not mine,” Trump wrote on Truth Social late last month. “I love that he is running!”

Behind closed doors, however, Trump is less sure. A Republican who was in the room with Trump this year as he reviewed polling said Trump was unsure how Kennedy would affect the race, asking the other people on hand whether or not Kennedy was actually good for his candidacy.

And after having mostly ignored Kennedy early in his campaign, Trump has stepped up his efforts to brand him as left-wing and make him Biden’s problem, suggesting that he and allies are concerned about Kennedy’s ability to attract Republican voters. In the post in which he said Kennedy was Biden’s political opponent, Trump called Kennedy “the most Radical Left Candidate in the race, by far,” someone who was “a big fan of the Green New Scam” and “other economy killing disasters.”

In a video monologue he posted to his social media page this month, Trump described Kennedy as being to Biden’s left but said Kennedy has “got some nice things about him” and “I happen to like him.”

“If I were a Democrat, I’d vote for RFK Jr. every single time over Biden because he’s frankly more in line with Democrats,” Trump said, adding: “I do believe that RFK Jr. will do very well. And I do believe he’s going to take a lot of votes away from crooked Joe Biden.”

Democrats have increased their attention on third-party contenders, standing up super PACs and other anti-spoiler efforts meant to kneecap independent challengers who could pull from Biden and reduce the vote share Trump needs to get over the top this fall. And in defiance of earlier conventional wisdom about the 2024 race, new polling shows that right now Trump might have the most to lose with Kennedy on the ballot.

An NBC News national poll released Sunday found that Kennedy cut deeper into Trump’s support than Biden’s. The survey found that 15% of voters who picked Trump in a head-to-head matchup with Biden switched to choose Kennedy in a five-way ballot test, while just 7% of those who initially selected Biden in the head-to-head switched to Kennedy when third-party candidates were added.

That trend meant Trump went from leading Biden by 2 percentage points in a head-to-head survey to trailing him by 2 points when the race is expanded to five named candidates, including Kennedy. The survey’s margin of error is plus or minus 3.1 percentage points.

Republican voters view Kennedy much more favorably than Democrats. The poll found that 40% of self-identified Republicans viewed Kennedy favorably, while 15% held negative views of him. Just 16% of Democrats had positive views of Kennedy, while 53% expressed negative views of him.

That’s in part the result of praise conservative media and Trump allies heaped on Kennedy when he was initially running in the Democratic primaries against Biden, as well as before this election cycle as Kennedy, a prominent vaccine skeptic, railed against the medical establishment and so-called social media censorship.

A Republican who worked on a door-knocking effort in an early state for a Trump primary opponent told NBC News that Kennedy often came up as the second choice among people who said they were backing Trump.

A changing posture

Trump himself has offered kind words for Kennedy in the past. In a June 2023 interview on “The Howie Carr Show,” Trump described Kennedy as “a commonsense guy.” Right-wing allies like Steve Bannon, Alex Jones and Roger Stone openly pined for Trump to pick Kennedy as his running mate.

The vibe is different now.

The pro-Trump PAC MAGA Inc. this month launched a “Radical F---ing Kennedy” website dedicated to promoting Kennedy’s left-wing positions. Kennedy, meanwhile, has criticized Trump from the right, hitting him for taking advice from Dr. Anthony Fauci during the coronavirus pandemic and for running up the deficit. He said another Trump term “would be bad for the country.”

“President Trump calls me an ultra-left radical,” Kennedy posted on X in response to the MAGA Inc. website. “I’m soooo liberal that his emissaries asked me to be his VP. I respectfully declined the offer.” (Trump’s campaign has denied that Kennedy was ever approached about being his running mate.)

“I am against President Trump, and President Biden can’t win,” Kennedy’s post continued. “Judging by his new website, it looks like President Trump knows who actually can beat him.”

On the whole, there have been public surveys showing both major-party candidates suffering more as a result of Kennedy’s campaign. The dynamic also may change depending on which state is being surveyed — and which states feature Kennedy on the ballot in November, a battle that is still in progress.

“Nobody has conducted more polls than I have on Kennedy and his place in the race — and continuously I have seen him draw equally from Biden and Trump,” said Jeremy Zogby, a managing partner at John Zogby Strategies who has polled for Kennedy’s campaign. “Sometimes a point or two towards one side in a poll and vice versa in another poll. The fact remains Kennedy has crossover appeal among those disaffected within both parties,” like the “double haters” who dislike both Biden and Trump.

Democrats have long worried that Kennedy’s association with his famous father and uncles will win over some liberals who are fond of the family. In addition, Kennedy for years gained acclaim as an environmental activist and an anti-corporate crusader, two causes that have him finding common ground with Democratic voters.

Last week, Biden held an event with Kennedy family members who touted Biden and warned of the danger Kennedy’s campaign posed. And Monday, the Democratic National Committee announced it was launching billboards in Arizona depicting Kennedy as a pro-Trump spoiler candidate.

A strategist working on the Democrats’ anti-third-party effort said the data shows Kennedy is clearly taking a slice from both major-party candidates, as well as a proportion of voters who wouldn’t be open to voting for either Trump or Biden.

“I think the data’s moved a little bit over the last month-plus,” this person said. “But it’s all on the margins. It’s tough to tell whether this is RFK appealing more to Trump voters or some Trump voters just looking for an off-ramp or both. Ditto on the Biden end — is this just reflecting the fact that Biden’s ticked up a few points?”

A Trump ally said Trump should hold off on hitting Kennedy for now, arguing there will be time in the fall to go after him as “too liberal for America” if the polling trends continue.

“The second you start attacking him or even addressing him, you start giving credibility to [him] and you start firming up those votes,” this person said, “At the moment, he’s irrelevant. As you get close and votes start hardening in terms of who people are voting for and when and why and how, then you’ve got to start making moves.”

In a statement, Trump’s campaign railed against Kennedy’s environmental positions and described him as “no independent” while also hitting Democrats for challenging his efforts to get on the ballot.

“RFK Jr. is an AOC lover and opposes really any human advancement, preferring that we all live in caves by candlelight, except of course supports charging stations for your $150,000 electric car that can only drive a few miles before dying just like his presidential campaign,” said Steven Cheung, Trump’s communications director.

Tony Lyons, a co-founder of the pro-Kennedy super PAC American Values 2024 and the president of Skyhorse Publishing, said there will be a “pendulum swinging back and forth” throughout the campaign that shows Kennedy at times being better for Trump and at other times boosting Biden’s candidacy.

Lyons said Kennedy will soon promote a 30-minute infomercial online that aims to hit back against the attacks he faces from his rivals.

“The fascinating part of it is that Trump says he’s ultra-left-wing,” Lyons said. “And Biden says that he’s ultra-right-wing.”

This article was originally published on NBCNews.com