President Donald Trump's Supreme Court nominee, Amy Coney Barrett, says she has given no commitments to the White House on how she will rule on Obamacare or election-related cases.
She has also declined to say whether she believes landmark rulings legalising abortion and gay marriage were properly decided.
Barrett opted not to tell her Senate Judiciary Committee confirmation hearing on Tuesday if she would step aside from a major Obamacare case to be argued on November 10 or in any disputes arising from the November 3 election - as Democrats have requested.
The marathon questioning gave the conservative US appellate judge a chance to respond to Democrats who oppose her because they fear she will cast a decisive vote in striking down the 2010 healthcare law formally called the Affordable Care Act and its protections for people with pre-existing conditions.
"I am not here on a mission to destroy the Affordable Care Act," Barrett said.
"I'm just here to apply the law and adhere to the rule of law."
Trump has asked the Senate, controlled by fellow Republicans, to confirm Barrett before Election Day.
He says he expects the Supreme Court to decide the election's outcome as he faces Democratic challenger Joe Biden.
Barrett said no one at the White House sought a commitment from her on how she would rule on that or any issue.
While Democrats were persistent in their questioning, the hearing retained a respectful tone and Barrett remained even-tempered while nimbly sidestepping questions on her views on abortion, LGBT rights, gun control and voting rights.
In the Obamacare case, Trump and Republican-led states are seeking to invalidate the law.
Barrett said the case centred on a different legal issue from two previous Supreme Court rulings that upheld Obamacare that she has criticised.
The law, signed by Barack Obama, has enabled millions of Americans to obtain medical coverage.
Democrats have blasted Trump for trying to kill Obamacare amid a deadly pandemic.
In declining to commit to stepping aside on politically charged cases in light of her nomination so near an election and comments made by Trump on the issues, Barrett said she would follow rules giving justices the final say on recusal amid questions about impartiality.
Republicans have a 53-47 Senate majority, making Barrett's confirmation a virtual certainty.
If confirmed, Barrett, 48, would give conservatives a 6-3 Supreme Court majority. She is Trump's third Supreme Court nominee.
Abortion rights advocates fear Barrett would vote to overturn the 1973 Roe v. Wade ruling that legalised abortion nationwide.
Asked about the ruling, Barrett said she would consider the usual factors on whether to overturn a precedent.
But Barrett indicated Roe v. Wade was not a "super-precedent" that could never potentially be overturned.
"I'm answering a lot of questions about Roe, which I think indicates Roe does not fall in that category," Barrett said.
"Scholars across the spectrum say that doesn't mean that Roe should be overruled but descriptively it does mean it is not a case that everyone has accepted."
Senator Dianne Feinstein, the panel's top Democrat, asked Barrett whether she agreed with her mentor, the late conservative Justice Antonin Scalia, that Roe v. Wade was wrongly decided and should be overturned.
After Barrett sidestepped, Feinstein told her that "it's distressing not to get a straight answer".
Barrett, a devout Catholic and a favourite of religious conservatives, said she could set aside her religious beliefs in making judicial decisions.