President Donald Trump has said he wants a new US Supreme Court judge to be sworn in “without delay”, following the death of the long serving liberal justice Ruth Bader Ginsberg.
Ginsburg, 87, died on Friday, just six weeks before the presidential election.
Trump’s Democrat rival, Joe Biden, insists the decision on her replacement must wait until after the vote.
The ideological balance of the nine-member court is crucial to its rulings on the most important issues in US law.
In 2016, Senate Republicans blocked Democratic President Barack Obama’s pick for the US top court. At the time, Senate Majority Leader Mitch McConnell justified the move on grounds that it was an election year.
But on Friday Senator McConnell said he intended to act on any nomination Trump made.
Ginsburg, a liberal icon and feminist standard-bearer, died of metastatic pancreatic cancer at her home in Washington DC, surrounded by her family. She was only the second-ever woman to sit on the US Supreme Court.
Supporters gathered outside the court on Friday night to pay tribute to the woman who had become affectionately known as “The Notorious RBG”.
What is the row about?
The appointment of judges in the US is a political question which means the president gets to choose who is put forward. The Senate then votes to confirm – or reject – the choice.
Ginsburg, who served for 27 years, was one of only four liberals on the nine-seat bench. Her death means that, should the Republicans get the vote through, the balance of power would shift decisively towards the conservatives.
Trump, who has already chosen two Supreme Court justices during his presidency, is well aware that getting his nominee in would give conservatives control over key decisions for decades to come. Justices can serve for life, unless they decide to retire.
“We were put in this position of power and importance to make decisions for the people who so proudly elected us, the most important of which has long been considered to be the selection of United States Supreme Court Justices. We have this obligation, without delay!,” he wrote on Twitter on Saturday.
Earlier, McConnell said in a statement – which included a tribute to Ginsburg – that “President Trump’s nominee will receive a vote on the floor of the United States Senate”.
The senator had argued in 2016 that “the American people should have a voice in the selection of their next Supreme Court Justice” which meant “this vacancy should not be filled until we have a new president”.
But now he says the Senate was within its rights to act because it was Republican-controlled, and Trump is a Republican president.
Democrats, however, began echoing McConnell’s words from 2016.
The Senate Democratic leader, Chuck Schumer, sent a tweet repeating his exact phrase, while Biden told reporters: “There is no doubt – let me be clear – that the voters should pick the president and the president should pick the justice for the Senate to consider.”
Ginsburg had also made her feelings clear in the days before her death.
“My most fervent wish is that I will not be replaced until a new president is installed,” she wrote in a statement to her granddaughter, according to National Public Radio (NPR).