Judge Ketanji Brown Jackson, president Joe Biden's nominee to serve on the US supreme court – she would be the first black woman to do so – has pledged to be independent in her actions, if ratified.
She also acknowledged that judges should have a “limited role” and be constrained by precedence.
In an opening statement on the first day of her confirmation hearing before the US Senate judiciary committee, Judge Jackson said she had served on the bench in lower courts for nearly a decade and took her responsibility and duty to be independent very seriously.
“I decide cases from a neutral posture. I evaluate the facts, and I interpret and apply the law to the facts of the case before me, without fear or favour, consistent with my judicial oath.”
She said she knew her role as a judge was a limited one, and the constitution empowered her to decide only cases and controversies that were properly presented. Her judicial role was further constrained by careful adherence to precedence.
Democrats on the committee defended Judge Jackson from criticism from Republicans, highlighting the historic nature of her selection and praising her record as a federal appellate and district court judge.
Republicans attacked some of her past rulings, sought to link her to advocacy groups on the left and looked for clarity on her judicial philosophy.
President Biden last month nominated Judge Jackson (51) for a lifetime position on the US Supreme court to succeed retiring liberal justice Stephen Breyer.
If ratified, her appointment would not change the ideological balance on the Supreme Court, which currently has a solid conservative majority.
The Democratic chairman of the judiciary committee, Senator Dick Durbin, said "not a single justice has been a black woman" in the court's history.
“You, Judge Jackson, can be the first. It’s not easy being the first. You have to be the best and in some ways the brightest. Your presence here today and your willingness to brave this process will give inspiration to millions of women who see themselves in you.”
Mr Durbin maintained attacks on Judge Jackson by some conservatives, who claimed she was “soft on crime”, were baseless and unfair. He said her judicial record showed she would not be a “rubber stamp” for president Biden.
The committee's top Republican Senator, Chuck Grassley, signalled his party would examine Judge Jackson's two-year stint earlier in her career as a lawyer defending low-income criminal defendants.
Republican senator Lindsey Graham questioned why outside groups pushing for left-leaning judges had backed her nomination.
Fellow Republican senator John Cornyn from Texas said he was "a bit troubled" by some of the arguments Judge Jackson had made when representing terrorism suspects.
“As someone who has deep respect for the adversarial system of justice, I understand the importance of zealous advocacy, but it appears that sometimes this zealous advocacy has gone beyond the pale. And in some instances, it appears that your advocacy has bled over into your decision-making process as a judge.”
Some of Judge Jackson's work as a public defender in a previous part of her career included challenging the detentions of alleged "enemy combatants" being held in Guantánamo Bay, Cuba, after the 9/11 attacks.
Tennessee Republican Marsha Blackburn said: "You used your time and talent not to serve our nation's veterans or other vulnerable groups, but to provide free legal services to help terrorists get out of Gitmo and go back to the fight."
Republican senator Josh Hawley said he intended to question Judge Jackson about what he considered to be relatively lenient sentences she meted out in child pornography cases.