Judge Ketanji Brown Jackson refused to define what a "woman" is because she's not a "biologist."
The Supreme Court nominee faced a second day of questions during her confirmation hearing on Tuesday.
Jackson was questioned for 12 hours by Republican senators of the Senate Judiciary Committee.
When asked to define a "woman" by Sen. Marsha Blackburn (R-Tenn) Jackson declined to answer.
Instead, she deferred to her lack of knowledge on the subject: "Not in this context. I can't... I'm not a biologist."
Blackburn responded, "The meaning of the word woman is so unclear and controversial that you can't give me a definition?"
Jackson, who was specifically nominated because she's a Black woman, also couldn't describe the inherent differences between a man and a woman.
The senator asked, "Do you agree with Justice [Ruth Bader] Ginsburg that there are physical differences between men and women that are enduring?"
Jackson replied, "Senator, respectfully, I am not familiar with that particular quote or case, so it's hard for me to comment as to whether or not—."
Blackburn interrupted, saying "Do you interpret Justice Ginsburg's meaning of men and women as male and female?"
"Again, because I don't know the case, I do not know how I'd interpret it. I'd need to read the whole thing."
"The fact that you can't give me a straight answer about something as fundamental as what a woman is underscores the dangers of the kind of progressive education that we are hearing about," Blackburn said.
"What message do you think this sends to girls who aspire to compete and win in sports at the highest levels?," the senator asked, referring to Lia Thomas (left), a male-bodied swimmer who won a women's NCAA championship for the University of Pennsylvania.
Republicans have expressed concern that, if Jackson is confirmed, the left's campaign to erase biological women will continue.
If Jackson is confirmed, she would become the first Black woman to serve as a justice on the U.S. Supreme Court.