Supreme Court Justice Ruth Bader Ginsburg has responded to Donald Trump's call for the top US court to stop impeachment.
"The president is not a lawyer," she told the BBC in an exclusive interview, adding: "He's not law trained."
In a wide-ranging conversation, she also said poor women were victims of restrictive abortion access.
The US president is expected to be impeached by the House of Representatives on Wednesday.
The House, controlled by the Democrats, accuses him of an abuse of power in his dealings with Ukraine.
Impeachment is like an indictment - the charges will then be sent to the Republican-controlled Senate for a trial, where senators act like jurors.
President Trump is expected to be acquitted there of the two charges he faces.
What did Ms Ginsburg say about impeachment?
Earlier this month, the president suggested in a tweet that the Supreme Court could step in.
"Radical Left has NO CASE. Read the Transcripts. Shouldn't even be allowed. Can we go to Supreme Court to stop?"
When the BBC's Razia Iqbal asked the justice what her reading of the constitution was in this context, she replied: "The president is not a lawyer, he's not law trained."
Ms Ginsburg was talking to the BBC at an event where she was awarded the Berggruen Prize for philosophy and culture, which is awarded annually to someone whose ideas "have profoundly shaped human understanding and advancement".
In the conversation, she also implied that senators who display bias should be disqualified from acting as jurors in the trial.
There was criticism over the weekend of Mitch McConnell, who leads the Republican party in the Senate, for saying an acquittal was a foregone conclusion.
When asked about senators making up their minds before the trial, the Supreme Court Justice said: "Well if a judge said that, a judge would be disqualified from sitting on the case."
What did she say about abortion access?
"I think society needs to be more active on this issue," she said.
"And the truth is that with all these restrictive laws, the only people who are being restricted are poor women."
Women with the means to travel to other states to get abortions were able to, she added.
Poor women bear the brunt of states' laws that restrict access, she said.
"They normally can't pay a plane fare or the bus fare, they can't afford to take days off of work to go."
Why is Ruth Bader Ginsburg important?
President Trump has appointed two judges since taking office, and the current court is seen to have a 5-4 conservative majority in most cases.
Ms Ginsburg, 86, is the oldest sitting justice on the Supreme Court, and has received hospital treatment a number of times in recent years.
As the court's most senior liberal justice, her health is closely watched.
Why is President Trump being impeached?
President Trump, it is alleged, pressured Ukraine to conduct two investigations for his own political gain and to the detriment of national security.
Democrats say he withheld $400m of military aid to Ukraine and a White House meeting with Ukraine's new leader.
The most serious allegation is that he asked for an investigation into his political rival Joe Biden, thereby enlisting foreign help to win the 2020 election.
He faces two articles of impeachment - abuse of power and obstruction of Congress.
He would become only the third US president to be impeached, but he denies any wrongdoing.
What is his latest defence?
In a six-page letter to the Democratic leadership on Tuesday, the president accused them of "subverting American democracy".
He repeated his claim that the phone call with the Ukrainian president, a call which is at the centre of the impeachment inquiry, was "totally innocent".
"Any member of Congress who votes in support of impeachment - against every shred of truth, fact, evidence and legal principle - is showing how deeply they revile the voters and how truly they detest America's constitutional order.
"Our founders feared the tribalisation of partisan politics and you are bringing their worst fears to life."
He ends the letter by saying that 100 years from now, people will understand and learn from this, "so that it can never happen to another president again".
President Trump signs it off with "Sincerely yours".
Want to find out more?
- A SIMPLE GUIDE: If you want a basic take, this one's for you
- GO DEEPER: Here's a 100, 300 and 800-word summary of the story
- WHAT'S IMPEACHMENT? A political process to remove a president
- VIEW FROM A SWING STATE: A bumpy ride for Democrat backing impeachment
- CONTEXT: Why Ukraine matters to the US
- FACT-CHECK: Did Ukraine interfere in the 2016 election to help Clinton?
- CASE FOR & AGAINST: What legal scholars say about Trump conduct