While President Donald Trump’s political opponents denounce his shutdown of the US government, they have another worry on their minds: Supreme Court Justice Ruth Bader Ginsburg has been diagnosed with lung cancer.

The 85-year-old underwent surgery on Friday to remove tumours spotted by a routine X-ray after she tripped in her office and broke three ribs.

That accident and resulting diagnosis raise the distinct possibility Ms Ginsburg’s days on the court are numbered, opening the way for Mr Trump to appoint a replacement and lock in the nine-judge panel’s conservative majority for decades to come.

“At a time when so few people, in Democrats’ minds, will stand up to Trump’s bullying style of leadership, a tiny octogenarian woman has stepped into the void and seemed to say: I’m not afraid of him at all,” writes CNN pundit Chris Cillizza.

Ms Ginsburg has made no secret of her loathing for the President.

“I can’t imagine what this place would be — I can’t imagine what the country would be — with Donald Trump as our president,” Ginsburg told The New York Times in a July 2016 interview .

“For the country, it could be four years. For the court, it could be — I don’t even want to contemplate that.”

Then-candidate Trump blasted Ms Ginsburg, accusing her of mental frailty and saying she should do the American people a favour stepping down.

“Justice Ginsburg of the U.S. Supreme Court has embarrassed all by making very dumb political statements about me. Her mind is shot – resign!” Mr Trump tweeted.

Ms Ginsburg subsequently apologised for her remarks while also making it clear she intends to remain on the court until the 2020 election, when a Democrat president might well win the Oval office and appoint a progressive jurist as her replacement.

“Post-surgery, there was no evidence of any remaining disease,” said Dr Valerie W Rusch, who led the surgery team at at Memorial Sloan Kettering Cancer Center in New York.

“Scans performed before surgery indicated no evidence of disease elsewhere in the body.”

Ms Ginsburg has not missed a day of oral arguments in her 25 years on the court and demonstrated her ongoing determination to block the Trump agenda by voting from her hospital bed on Friday against the administration’s bid to limit the grounds on which migrants can apply for asylum in the US.

Ms Ginsburg’s vote helped doom the restrictions, but Democrats wonder just how much longer she can stand as a barrier to Mr Trump’s ambitions.

-with AAP