WATCH: Democrats dismiss Biden-Kennedy 2024 primary debate: 'Fringe candidate'

Robert F. Kennedy Jr. is stepping up his campaign to challenge President Joe Biden for the 2024 Democratic nomination, but Democrats in Congress are already shrugging him off as a "fringe candidate" and distancing themselves from the idea of a debate between the two.

Party officials have already poured cold water on the possibility of holding debates during this election cycle, as is the norm for the side with an incumbent White House candidate.

Kennedy – the nephew of former President John F. Kennedy – is widely regarded as a long shot against Biden. But he’s tried to make the case that he could beat both former President Donald Trump and Florida Gov. Ron DeSantis, the two GOP front-runners, and in recent days he even swung at Biden himself for a foreign policy that Kennedy denounced on Twitter Spaces as "very bellicose, pugnacious and aggressive."

But several House Democrats interviewed by Fox News Digital have shrugged off Kennedy’s challenge, with their responses ranging from ambivalence to outright dismissal.

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"No," Rep. Glenn Ivey, D-Md., said bluntly when asked whether the Kennedy scion should get to debate the sitting president. "I, you know, love the Kennedy family. I was a huge fan of his father, in fact, he was an inspiration to me. But I don’t think he’s a serious candidate. I think Joe Biden’s going to be our nominee, and he deserves to be."

Rep. Zoe Lofgren, D-Calif., was equally opposed to the idea, saying, "He’s a fringe candidate, so I don’t think Biden is going to necessarily debate fringe candidates. Nor should he."

Some, like Reps. Richard Neal and Seth Moulton, both from Kennedy's home state of Massachusetts, were more circumspect in their hesitation.

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"Well, that’s up to Joe Biden, I mean, it seems to me Kennedy is on the margins here," Neal told Fox News Digital. "And I noticed the Republicans have already put out markers on who will qualify for debates, so I think that’s premature, but it’s up to the administration."

Moulton said, "You have established party processes for this. But I think the bar is for everybody to be considered a, you know, serious candidate with some real traction before they get on the debate stage."

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"It’s pretty uncommon for an incumbent to participate in a primary debate, but I don’t know how far back that tradition goes," Rep. Jeff Jackson, D-N.C., said.

In fact, no incumbent president has entertained a primary debate since they were first broadcast to the public via radio in 1948.

Reps. Jamaal Bowman, D-N.Y., and Sheila Jackson Lee, D-Texas, made clear that whether that tradition is broken now is not up to congressional lawmakers.

"It’s up to the president if he wants to do it or not. The president has a very strong record to stand on, so whoever decides to debate him, they’re going to have an uphill climb," Bowman said. "So, it’s up to the president to decide, I don’t know."

Jackson Lee said it was for the relevant parties to hash out, saying, "My view is the campaign is on."

"Each campaign camp will decide what is best for the American people, and I’m going to yield to the decisions the campaign camps make. I want the best candidate out there, and let the campaign camps get together and share their views with the American people," Jackson Lee added.

Kennedy said earlier this year it was "unfortunate" that the national party would not hold primary debates. But a recent Fox News poll shows Biden with a commanding lead over Kennedy, whose skepticism about vaccines has alienated a sizable amount of Democrat voters.

The late May survey shows Biden with 62% support from left-wing primary voters, Kennedy has 16% and author Marianne Williamson is a distant third with 8%.