For months, Robert F. Kennedy Jr. has said he plans to continue his long-shot challenge against President Biden in the Democratic primary rather than dropping out to launch a third-party bid.
But lately Mr. Kennedy’s message has seemed to shift, including publicly telling a voter who asked about his plans that he was keeping his “options open.”
If Mr. Kennedy does decide to leave the party of his famous father and uncles to run in the general election, one potential landing spot may be the Libertarian Party, which at the moment lacks a widely known candidate but has excelled at securing ballot access.
In July, Mr. Kennedy met privately with Angela McArdle, the chair of the Libertarian Party, at a conference they were both attending in Memphis — a meeting that has not previously been reported.
“He emphasized that he was committed to running as a Democrat but said that he considered himself very libertarian,” Ms. McArdle said in an interview, adding that they agreed on several positions, including the threat of the “deep state” and the need for populist messaging. “We’re aligned on a lot of issues.”
“My perspective is that we are going to stay in touch in case he does decide to run,” Ms. McArdle said. “And he can contact me at any time if that’s the case.”
In a June interview with the libertarian magazine Reason, Mr. Kennedy acknowledged his ideological disagreements with the party — including on issues like environmental protection, abortion and civil rights — while also saying, “I’ve always been aligned with libertarians on most issues.”
In a general election, Democrats worry that a third-party run by Mr. Kennedy could draw votes away from Mr. Biden and help elect former President Donald J. Trump. They have expressed similar concerns about No Labels, the bipartisan group trying to recruit a moderate candidate for a third-party run, and also about the progressive scholar Cornel West, who is already in the race to lead the Green Party’s ticket for 2024.
Matt Bennett, a co-founder of the centrist Democratic group Third Way, has been helping coordinate Democratic efforts to stop the No Labels effort. He said the hope in the party has been that Mr. Kennedy would “go away” after losing primaries to Mr. Biden.
“It would be very bad” if Mr. Kennedy runs as a Libertarian, Mr. Bennett said. “We’ve been very clear that third parties in close elections can be very dangerous and would almost certainly hurt the president. That would be true of a No Labels candidate and it would be true of R.F.K.”
Dennis Kucinich, Mr. Kennedy’s campaign manager, said there was “no truth” to the idea that Mr. Kennedy could run as a Libertarian. He said the meeting with Ms. McArdle simply offered “further proof of Mr. Kennedy’s appeal across the political spectrum.”
“We have not sought the favor of any other political party,” Mr. Kucinich said.
Ms. McArdle said that the meeting, at the libertarian FreedomFest convention, had been requested by Heal the Divide, a pro-Kennedy super PAC, and that she spoke with Mr. Kennedy for nearly an hour but had not had further meetings. He separately met with other leaders of the libertarian movement at the conference, she added.
Mr. Kennedy, who is perhaps best known for his conspiracy theories about the safety of vaccines, would likely become a favorite to win the Libertarian nomination given his national name recognition.
In the Democratic primary, Mr. Kennedy is trailing Mr. Biden by roughly 50 points, according to 538’s national polling average, and his bid against the incumbent president is not seen as competitive. He has argued that Mr. Biden’s allies at the Democratic National Committee are trying to squeeze him out of the race, including by moving to hold the party’s first primary in the Biden-friendly state of South Carolina.
In past comments, Mr. Kennedy committed to sticking with the party long identified with the Kennedy clan. Late last month, Mr. Kennedy told Fox News that his mission was to “summon the Democratic Party back to its traditional ideals.”
But more recently, Mr. Kennedy has seemed to hint that could change. In response to a South Carolina voter’s question this month about whether he would launch an independent bid, Mr. Kennedy said the D.N.C. is “trying to make sure that I can’t participate at all in the political process, and so I’m going to keep all my options open,” according to ABC News.
Surveys have shown that a growing number of Americans are unhappy with both major political parties. But they have also expressed little appetite for third parties.
In 2016, the moderate Gary Johnson, a former Republican governor of New Mexico, and his running mate, former Gov. William F. Weld of Massachusetts, received 3.3 percent of the popular vote. That was the best performance by a third-party ticket since Ross Perot ran on the Reform Party ballot in 1996.
In an interview on Friday, Mr. Johnson said he thought Mr. Kennedy might struggle to win over Libertarian voters given that he is now a Democrat. But he said he would favor Mr. Kennedy over both the current and former presidents in a general election, should they all win their respective nominating contests.
“If Kennedy manages to get through the process and become the Libertarian nominee, I’d vote for him in a heartbeat,” Mr. Johnson said, “because he’s not Biden and he’s not Trump.”
Reid J. Epstein contributed reporting from Washington. Kirsten Noyes contributed research.