Donald Trump’s move to replace the late Supreme Court Justice Ruth Bader Ginsburg before the presidential election is an “abuse of power”, his Democratic rival Joe Biden says.
Mr Trump has said he will nominate a woman to replace the longstanding liberal justice.
Mr Biden has urged Senate Republicans to delay a confirmation vote.
Ginsburg, a liberal icon and feminist standard-bearer, died on Friday, aged 87.
The appointment of judges to the Supreme Court is a political decision in which the president chooses who is put forward. The Senate then votes to confirm – or reject – that choice.
Democrats fear Republicans will vote to lock in a decades-long conservative majority on the country’s highest court.
The ideological balance of the nine-member court is crucial to its rulings on the most important issues in US law.
Mr Biden on Sunday said the president had “made clear this is about power, pure and simple.”
“The United States constitution allows Americans the chance to be heard – and their voice should be heard… they should make it clear, they will not stand for this abuse of power,” he said.
“I appeal to those Senate Republicans – please follow your conscience, let the people speak, cool the flames that have been engulfing our country.”
Mr Biden said that if he won the presidential election, Mr Trump’s nominee should be withdrawn.
He said he would then consult senators from both parties before putting forward his choice.
He has not named any potential nominees, but said his first choice “will make history as the first African American woman on the court.”
Two Republican senators, Susan Collins and Lisa Murkowski, have backed a delay in the vote.
Maine Senator Ms Collins said she had “no objection” to the process of reviewing a candidate beginning now, but that she did not believe the Senate should vote on the candidate prior to November’s election.
Alaska Senator Ms Murkowski said she “did not support taking up a nomination eight months before the 2016 election” and believed the “same standard must apply” now.
Both women have broken away from party lines in the past, including on issues like abortion rights. Ms Collins faces a tough re-election bid this year and is trying to defend her reputation as a moderate. -BBC