The surprising success of a maverick presidential run by a scion of the Kennedy family, Robert F. Kennedy Jr., points to a problem that Democrats are doing their best to ignore: Few in the party’s rank and file are jazzed about the incumbent, and some of them are willing to embrace even the kookiest of candidates as a result.

Despite spending little money and being largely shunned by the mainstream press — silenced mid-interview in some cases — Mr. Kennedy’s poll numbers keep ticking up. Before he formally announced his candidacy April 19, a Morning Consult poll had him at 10 percent among Democratic voters. Just more than a week later, he was polling at 21 percent in an Emerson College poll. 

It’s not just Mr. Kennedy chipping away at President Biden’s poll showing. The crystal-loving “spiritual leader” who ran unsuccessfully in 2020 but dropped out after polling at a little over 1 percent, Marianne Williamson, has inched up to 9 percent this time around in one Fox News poll of Democratic primary voters. Nearly a third of Democratic voters, if the polls are to be believed, appear desperate to cling to anyone other than the party’s current standard-bearer.

“If Kennedy can get his message out I think he could cause much bigger problems for the incumbent than currently thought in most quarters,” a former ABC News political director who now appears regularly on the conservative Newsmax network, Mark Halperin, wrote on his Substack newsletter recently. “If he becomes the protest candidate repository for the giant pool of Democratic primary voters who are unenthused about Biden-Harris, watch out.”

The last time a Kennedy challenged an incumbent Democratic president — in 1980 — that incumbent went on to lose the general election. That year, Mr. Kennedy’s uncle, Ted Kennedy, challenged President Carter in the Democratic primary, eventually winning 12 states and leaving the nomination in limbo until the second night of the party’s convention. It was the last time an incumbent party’s nomination was undecided going into a convention. 

Mr. Kennedy has a near-zero chance of upending the apple cart entirely — Mr. Biden polls at between 60 and 70 percent in those same polls and enjoys the backing of most of the party establishment — but with half of Democrats telling pollsters that they would prefer that the president not run for re-election, the surprise showing for the two outliers is bound to be giving Mr. Biden’s campaign staff ulcers. That they even feel the need to say openly that an incumbent president is not going to debate the likes of Mr. Kennedy and Ms. Williamson is a sign of how much of a thorn in their sides the wanna-be challengers have become.

Although he is running as a Democrat, Mr. Kennedy has taken some positions decidedly out of the liberal mainstream of the moment. Since announcing, he has said he opposes allowing transgender men to compete against female athletes, and expressed skepticism about America’s support for Ukraine. He has attacked Mr. Biden for what he calls the “chaos” at the border, and suggested that billionaires are exploiting climate change hysteria in order to impose totalitarian control over society.

“Climate issues and pollution issues are being exploited by, you know, the World Economic Forum and Bill Gates and all of these big, you know, mega-billionaires, the same way that Covid was exploited, to use it as an excuse to clamp down top-down totalitarian controls on society,” Mr. Kennedy told talk show host Kim Iversen recently.

It is on the issue of vaccines — all vaccines, not just Covid vaccines — that Mr. Kennedy deviates from the Democratic consensus the most. His diatribes against public health officials such as Anthony Fauci over Covid vaccine mandates have drawn accolades from the likes of a high-profile advisor to President Trump, Steve Bannon, and a popular conspiracy theorist, Alex Jones. ABC News went so far as to excise his comments on the topic from a recent interview before airing it, telling viewers that “during our conversation, Kennedy made false claims about the Covid-19 vaccines. We’ve used our editorial judgment in not including extended portions of that exchange in our interview.”

A research analyst at the polling firm Echelon Insights, Avery James, says he believes Mr. Kennedy’s name at least partially explains his apparent popularity, especially among older voters. In recent polls by the firm, he tells the Sun, some 13 percent of voters under 50 said they have never heard of Mr. Kennedy, compared to only 1 percent of those over 50 who say the same. Mr. Biden’s supporters are probably more worried about their candidate’s polling among young voters than they are about fringe candidates who appear to be surging in these early days.

“People like the Kennedy name, and they might like RFK Jr.,” Mr. James says. “But I suspect Biden’s real fear isn’t associated with the past so much as the future. He has to turn out the whole coalition, which includes convincing enough young Democratic voters that he represents their interests. Judging by our latest omnibus and last year of continuous polling, I’d say that’s a murkier prospect right now.”