Robert F. Kennedy Jr.'s candidacy poses more of an issue for Donald Trump than it does for Joe Biden, according to a poll conducted by NBC News.

When voters were asked solely about Biden and Trump, the former president is narrowly beating the incumbent 46% to 44%. When third-party candidates are introduced to the race, however, Biden pulls ahead of Trump.

In a five-way race, Biden received 39% of the votes, followed by Trump at 37%, Kennedy at 13%, Jill Stein at 3 percent and Cornel West at 3 percent. Fifteen percent of the respondents who picked Trump in a two-way race picked Kennedy when the options were expanded. By contrast, only 7 percent of those who initially picked Biden switched to Kennedy.

"At this stage, [Kennedy's] appeal looks to be more with Trump than Biden voters," Democratic pollster Jeff Horwitt told NBC News.

While Kennedy remains a longshot candidate, the third-party challenger has received attention from both Trump and Biden, in recent weeks.

In a video posted to Truth Social, Trump described Kennedy as "the most radical left candidate in the race," but also said that if he were a Democrat he'd choose Kennedy over Biden. In response, Kennedy claimed that Trump asked him to join the Republican ticket as the vice presidential candidate.

For his part, Biden has touted endorsements from a number of Kennedy's relatives — including six of his siblings. In a campaign ad, featuring members of the political dynasty, Kennedy's brother Chris described Biden as "the RFK of his generation."

Kennedy has previously drawn the ire of his family members, in part due to his history of promoting scientifically inaccurate information about vaccines. He has repeated the disproven claim that vaccines cause autism and is one of the most prominent voices in the anti-COVID-19 vaccine movement.