Senators in both parties are warning that Robert F. Kennedy Jr. may end up tipping the presidential election to either former President Trump or President Biden, but Democrats are expressing more worries he could be a spoiler candidate than Republicans.

Sen. Mazie Hirono (D-Hawaii), one of President Biden’s most outspoken defenders on Capitol Hill, said it’s hard to predict how exactly Kennedy will impact the race for the White House.

But she expressed concern that he will hurt Biden more because of his relationship to former President Kennedy, his uncle, and former attorney general and presidential candidate, Robert F. Kennedy — two legendary figures in the Democratic Party.

“I think he’s basically helping Trump,” she said. “I think he’s being used.”

Democrats were shocked when Kennedy recently declared Biden is a “much worse threat to democracy” than Trump because he is the “first candidate in history, the first president in history, that has used federal agencies to censor political speech” and to “censor his opponent.”

The claim sounded like an argument Trump would make at a political rally, the Democrats said.

In announcing his running mate, Nicole Shanahan, a wealthy Democratic donor, Kennedy declared the values of the Democratic Party have changed since the days of Camelot.

Sen. Debbie Stabenow (D-Mich.), who represents a key presidential battleground state, conceded Kennedy’s “last name would have the potential of hurting Biden.”

At the organization level, Democrats are also signaling their concerns.

The Democratic National Committee has set up a team led by former White House counsel Dana Remus to track Kennedy’s efforts to get on the battle in swing states. Biden’s allies at the DNC are also stepping up efforts to define Kennedy as a radical who shares Trump’s embrace of the anti-vaccine movement.

Stabenow argued Kennedy is more similar to Trump because “the reality is that Kennedy believes in conspiracies and doesn’t believe in science, and that’s very aligned with Donald Trump.”

Trump came under fire while president for promoting a video claiming hydroxychloroquine, the anti-parasite medicine, could cure COVID-19, a claim Trump’s top health adviser, Anthony Fauci, debunked as false.

More recently, Trump promoted the claim that his GOP primary rival Nikki Haley was ineligible to serve as president because her parents were not U.S. citizens when she was born. Before then, he famously fueled the false claim that former President Obama wasn’t born in the United States.

Republican senators warn Kennedy could pull some votes away from Trump, but some also suggest he could hurt Biden more than the former president.

Sen. John Hoeven (R-N.D.) said “both Biden and Trump are making sure they address him being in the race, which is smart.”

“He may take votes from Trump, he may take votes from Biden. All in, I think he would take more votes from Biden,” Hoeven said.

“Trump is putting out there very clearly now: Don’t be confused folks, this guy is liberal,” Hoeven said. “My general sense is that the Democrats are more worried about Kennedy than in general Republicans are.”

Pennsylvania Lt. Gov. Austin Davis warned in a press call sponsored by the DNC last month that “all [Kennedy] can do is take away votes from President Biden and make it easier for Donald Trump to win.”

Ross K. Baker, a political science professor at Rutgers University, said “it makes intuitive sense” that Kennedy’s “basic rationale for running and strategy is to evoke memories particularly of older Americans of his father and his uncle.”

“He’s able to take advantage of people who somehow think that he’s a reincarnation [of them], that he’s got the Kennedy magic,” he said.

But Baker pointed out that many in Kennedy’s family have expressed opposition to his presidential bid.

Four of his siblings, former Maryland Lt. Gov. Kathleen Kennedy Townsend (D), former Rep. Joseph Kennedy II (D-Mass.), Rory Kennedy and Kerry Kennedy, signed a statement calling his challenge to Biden “dangerous to our country.”

A super PAC supporting Kennedy says it has enough signatures to get him on the ballot in several key swing states — Arizona, Georgia, South Carolina and Michigan.

And the Kennedy campaign says it has enough signatures to qualify in Nevada, New Hampshire and Utah.

They’re trying to get on the ballot in all 50 states.

Kennedy’s surprising traction with voters and grassroots donors is creating an unpredictable dynamic that reminds lawmakers in both parties of the spoiler role Ross Perot was thought to have played in 1992, when former President Clinton defeated incumbent President George H.W. Bush.

Perot won 19 percent of the popular vote that year, even though he didn’t win a single state or electoral vote. He was widely credited at the time with costing Bush his reelection to the White House, though some political scientists have later questioned whether that really happened.

It’s difficult to know the precise impact because analysts can’t know for sure how voters who supported him would have cast their ballots if he wasn’t in the race.

But in key swing states, such as Georgia, Nevada, Ohio and Pennsylvania, Perot won a considerably greater share of the vote than Clinton’s margin of victory.

For example, in Ohio, which Clinton won with 40 percent of the vote compared to Bush’s 38 percent share, Perot won 21 percent. In Georgia, Clinton barely carried the state with 43.5 percent of the vote, while Bush won 42.9 percent and Perot won 13 percent.

Centrist Sen. Joe Manchin (D-W.Va.), who flirted with an independent bid for president earlier this year before deciding against it, said Kennedy’s candidacy could “hurt both ways.”

He noted that a Kennedy campaign staffer said her “No. 1 priority” was to prevent Biden’s reelection.

The staffer, Rita Palmer, was later fired by the campaign for “misrepresentation.”

“I think it’s a toss of the coin,” Manchin said of Kennedy’s impact on the race. “What we don’t know,” Manchin added, is whether Kennedy will bring out people “who wouldn’t normally vote.”

Manchin warned the race is so close “that anybody could” swing the race one way or the other, including long-shot candidates Jill Stein and Cornel West.

He said the angry reaction from Democrats to his potential presidential bid shows how members of his party feel a third-party candidate might affect the race.

“They went after No Labels like a rabid shark,” he said of the barrage of Democratic attacks against the centrist group that tried to persuade him and other prominent figures, such as Larry Hogan, the moderate former Republican governor of Maryland, to run against Biden.