Democratic presidential candidate Robert F. Kennedy Jr. is questioning whether President Biden has the "vigor" to handle the "very rigorous job" of president of the United States.

In an interview with Fox News Digital, the long-shot Democratic presidential primary challenger urged the 80-year-old Biden to hold "unscripted meetings and interactions with voters" so Americans can determine if the president "is up to the job."

Biden has faced questions and concerns over his age ever since he made history in 2020 when he became the oldest person ever elected president. If the president wins re-election next year, he would be 82 at his second inauguration and 86 at the end of his second term.

Polls have long indicated that Americans have concerns over Biden's age. The most recent survey on the issue from CNN indicated that roughly three-quarters of Americans said they were seriously concerned that the president's age might negatively affect his current level of physical and mental competence and his ability to serve out another full four-year term if re-elected.

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President Joe Biden speaks at the Democratic National Committee Winter Meeting, Friday, Feb. 3, 2023, in Philadelphia. (AP Photo/Patrick Semansky)

President Joe Biden speaks at the Democratic National Committee Winter Meeting, Friday, Feb. 3, 2023, in Philadelphia. (AP Photo/Patrick Semansky) (AP )

Republican presidential contenders have repeatedly questioned Biden over his age.

GOP White House candidate and Florida Gov. Ron DeSantis said Tuesday in a CBS News interview that "I think that’s absolutely a legitimate concern. The presidency's not a job for someone that’s 80 years old." 

Now, it appears the 69-year-old Kennedy is taking a page from the same political playbook.

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"A lot of people will say that ‘well President Biden is surrounded by very good people who will run the country even if he can’t,’ but I don’t think that’s a good way for democracy to work," Kennedy told Fox News on Tuesday.

The environmental lawyer, high-profile vaccine critic, and a scion of arguably the nation’s most famous political dynasty, raised concerns that "unelected people in lanyards are going to be making critical decisions in a very, very difficult time in our history."

Robert F. Kennedy questions Biden over his age and ability to serve as president

Robert F. Kennedy Jr, who's primary challenging President Biden for the 2024 Democratic nomination, speaks to supporters at Robie's Country Store, in Hooksett, New Hampshire on Sept. 12, 2023 (Fox News - Paul Steinhauser)

"It’s important for the American people to know that their president has the vigor to handle this very rigorous job and I think there are enough doubts about that now that President Biden really needs to come out and have an unscripted meetings and interactions with voters, that he needs to do some town halls and retail politics and hopefully a debate so that the American people can make a choice about whether or not the president is up to the job," Kennedy said.

Kennedy spotlighted concerns over Biden's age after being asked about comments he made in an interview last week when he said people should be voting for "a president who we expect to complete the term."

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A national Democratic strategist, who asked to remain anonymous to speak more freely, took aim at Kennedy, sarcastically telling Fox News that it's "absolutely shocking that the pro-Russia, pro-gun, anti-vaxxer candidate pretending to be a Democrat is parroting the same tired, worn out Republican talking points. Give me a break."

Kennedy was interviewed ahead of a campaign event with voters at Robie's General Store in Hooksett, New Hampshire, which has long been a must stop in the early voting state by White House contenders.

The candidate reiterated his claims that he's not getting a fair shake from the Democratic National Committee (DNC).

"The DNC’s own rules say that they have to be neutral during the election but they are very open about having abandoned their neutrality and they’ve made a series of rules that make it almost — if those rules continue — it makes it almost impossible for anybody except Joe Biden to win the primary process," Kennedy charged.

And he repeated his argument that the DNC is "disenfranchising the Democratic voters" in the primary process.

"We live in a time when a lot of people believe the system is rigged, that democracy is no longer functioning," Kennedy warned. 

He urged that "the Democratic Party ought to be a temple for Democracy. It ought to be role modeling democracy. Most Americans assume that the candidate who wins should be the candidate who gets the most votes and that we should have rules that actually reflect that assumption."

Kennedy's concerns with the DNC center on its often at odds roles of being the impartial referee of the presidential nominating process while at the same time following longstanding tradition and precedent of both major national party committees in endorsing and supporting a sitting president's re-election campaign. 

Robert F. Kennedy stands alongside bust of his late uncle, President John F. Kennedy

Democratic presidential candidate Robert F. Kennedy Jr. stands alongside a bust of his late uncle, President John F. Kennedy, outside city hall in Nashua, New Hampshire, on June 20, 2023. (Fox News (Paul Steinhauser))

The candidate's complaints about a Democratic nomination process that favors the president have been coupled in recent days with what appear to be unfounded election rigging allegations against the DNC 

DNC Chair Jaime Harrison responded to Kennedy's allegations in a letter obtained Tuesday by Fox News.

Harrison wrote that it "is clear that there are serious misunderstandings of the Democratic nominating process that are important to correct."

"I am hopeful that a meeting with our Delegate Selection leadership team will prevent future instances of voters receiving erroneous information that could cause confusion about the equity of the Democratic nominating process," the DNC chair added.

The latest polls in the Democratic presidential nomination race indicate that Kennedy and fellow primary challenger Marianne Williamson face steep uphill climbs against Biden.

But Kennedy does appear to be gaining some support among independent voters, Libertarians, and even some Republicans.

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Asked if he would consider a third party White House run if he doesn't succeed in the race for the Democratic nomination, Kenney said: "we are hoping that I could run in the Democratic Party and at this point that’s the plan."

Kennedy reiterated that when it comes to the Democratic nomination race, "I’m very confident that if I’m given a fair shot, that I’m going to win."

Get the latest updates from the 2024 campaign trail, exclusive interviews and more at our Fox News Digital election hub.