Trump Attacks R.F.K. Jr., a Third-Party Wild Card

Former President Donald J. Trump’s views on Robert F. Kennedy Jr. have vacillated over the last year. When Mr. Kennedy was running against President Biden in the Democratic primary, Mr. Trump praised him as “very smart.”

Former President Donald J. Trump attacked Robert F. Kennedy Jr., the independent presidential candidate, on Wednesday morning, casting Mr. Kennedy as a liberal Democrat in disguise while also seeming to back him as a spoiler for President Biden’s campaign.

Mr. Trump, the presumptive Republican presidential nominee, pointed in particular to Mr. Kennedy’s views on climate change and the environment, writing on his social media site that Mr. Kennedy was more “radical Left” than Mr. Biden.

Yet he also professed support for Mr. Kennedy’s campaign, claiming that Mr. Kennedy would be likely to siphon votes from Mr. Biden. “I love that he is running!” Mr. Trump concluded.

Mr. Trump’s post, which came a day after Mr. Kennedy announced his running mate, underscores the political wild card that is Mr. Kennedy’s bid. Even as Mr. Trump asserted that Mr. Kennedy’s independent campaign would be a boon to his own effort to beat Mr. Biden, two Trump campaign officials said they had seen polling that showed Mr. Kennedy drawing support from independent voters in a way that could be equally detrimental to both Mr. Trump and Mr. Biden.

Though Mr. Kennedy will face challenges getting on the ballot in several states, it is possible that his campaign could tip the scales in battlegrounds where the margins of victory have been narrow in recent election cycles.

Mr. Kennedy’s campaign did not respond to a request for comment. But on Tuesday, he made clear his intention to court voters who have soured on both candidates. “Our campaign is a spoiler all right,” he said during his announcement. “It is a spoiler for President Biden and for President Trump.”

Underlying Mr. Kennedy’s possible appeal are positions that defy easy political categorization or are inconsistent. A former environmental lawyer, Mr. Kennedy started his presidential campaign last year as a Democrat challenging Mr. Biden in the primary. After six months, he announced he would run as an independent candidate instead.

Mr. Kennedy has voiced support for the Green New Deal and has backed environmental policies favored by the left that would limit the use of fossil fuels. But he opposes military assistance for Ukraine in its war against Russia, putting him at odds with mainstream Democrats and aligning him more closely with many on the right, including Mr. Trump.

After backing a federal abortion ban last year, Mr. Kennedy immediately backtracked and said he supported a woman’s right to choose, without offering specifics. Democrats are expected to make protecting reproductive rights central to Mr. Biden’s re-election campaign.

Mr. Kennedy, long a vaccine skeptic, also rose to prominence during the coronavirus pandemic, when he railed against vaccine mandates and lockdown measures. His anti-vaccine views have been largely embraced by the Republican Party under Mr. Trump, whose administration spurred development of the Covid-19 vaccine. Mr. Trump frequently denounces mask and vaccine mandates during his rallies.

Boosted in part by his family name, Mr. Kennedy has had a remarkably strong showing in some national and state polls for an independent candidate. A national Fox News poll conducted last month found Mr. Kennedy’s polling at 13 percent.

But data shows that poll results tend to inflate support for independent and third-party candidates, and it remains to be seen whether Mr. Kennedy’s backing will hold down the stretch.

Surveys have also left an unclear picture over which major-party candidate might be more damaged by Mr. Kennedy’s presence on the ballot. Last year, polls of six battleground states by The New York Times and Siena College found that Mr. Kennedy pulled similar numbers of voters from Mr. Biden and Mr. Trump.

The Democratic Party, which sees Mr. Trump’s base of support as sturdier than Mr. Biden’s, has mounted an effort to blunt the threat that third-party and independent candidates might pose to the president’s re-election bid.

The party is increasingly arguing that Mr. Kennedy’s campaign is a “spoiler” propped up by allies of Mr. Trump. Mr. Biden’s backers have also pointed to Mr. Kennedy’s views to show that he is out of line with mainstream liberal values.

“Donald Trump is saying the quiet part out loud: R.F.K. Jr. is a spoiler candidate,” Matt Corridoni, a spokesman for the Democratic National Committee, said in a statement.

Republicans have not mounted the same kind of undertaking. But Mr. Trump’s statement suggests a similar effort to define Mr. Kennedy as voters become more familiar with him.

The former president’s views on Mr. Kennedy have vacillated over the last year. When Mr. Kennedy was challenging Mr. Biden in the Democratic primary, Mr. Trump, who once appointed Mr. Kennedy to a commission on vaccines, praised him as a “very smart person.”

“I like him a lot. I’ve known him for a long time,” Mr. Trump said in an interview in September. “He’s very much a libertarian in a certain way. And I think I have certain qualities along those lines, too, if you want to know the truth.”

But after Mr. Kennedy opted instead to run as an independent candidate, the Trump campaign and the Republican National Committee quickly began tying Mr. Kennedy to the left, arguing that his independent bid was an effort to deceive voters about his politics.

Rebecca Davis O’Brien contributed reporting.