Presidential candidate Robert F. Kennedy Jr. said in a new interview that he does not support transgender women participating in women's sports.
A Democrat told CNN on Saturday that "biological men" threaten the integrity of women's athletics.
"I am biologically against male participation in women's sports," said Kennedy, 69.
"I think women have worked so hard to advance women's sports over the past 30 years. I've seen it and I don't think it's fair."
Kennedy, who announced his candidacy on April 19, said he and President Biden were "real at odds" over his lack of support for transgender participation.
Earlier this month, the Biden administration unveiled a proposal to prevent district schools and colleges from banning transgender athletes entirely.
However, last week, House Republicans passed a bill that would bar transgender athletes from participating in women's sports by changing Title IX protections that apply only to female biologists.
No Democrats supported the measure, although ten abstained.
President Biden has said he would veto the bill if it were on his desk.
Jr. Allowing "biological men" to participate in women's sports affects the safety of women's athletics. Polaris
The case continued to gain momentum on the national stage with the arrival of NCAA defending champion Leah Thomas.
Kennedy joined Marianna Williamson in the Democratic presidential primary against incumbent Joe Biden, who has said he plans to run for re-election but has not launched an official campaign.
In the months leading up to his announcement, Kennedy had become one of the leading opponents of the vaccine.
Robert Kennedy, grandson of the late President John F. Kennedy and son of the Attorney General and former presidential candidate of the United States, said: "I think our country is going to hell and that is why I am nominated." The 1968 presidential election that killed Robert Kennedy.