Republican politicians and presidential candidates look set to block a move by US President Barack Obama to fill the seat left by the late conservative Justice Antonin Scalia on the Supreme Court bench.
The position is a lifetime appointment that would help decide some of the most divisive issues facing Americans.
The next justice could tilt the balance of the nation's highest court, which was left with four conservatives and four liberals. The vacancy quickly became an issue in the 2016 presidential race.
"We ought to make the 2016 election a referendum on the Supreme Court," US Senator and Republican presidential candidate Ted Cruz said on NBC's Meet the Press on Sunday (local time).
The normally nine-justice court is set to decide this year its first major abortion case in nearly a decade, as well as cases on voting rights, affirmative action and immigration.
Scalia, 79, died on Saturday at a West Texas resort from an apparent heart attack, Texas television station WFAA-TV reported on Sunday, citing a Texas county judge.
Obama, a Democrat, said on Saturday that he would nominate someone to fill the empty seat, setting up a battle with the Republican-controlled Senate, which must approve any nominee.
Republicans quickly vowed not to act on the vacancy until Obama's successor takes office next January.
Senate Democratic leader Harry Reid said failure to act would be a "shameful abdication" of the Senate's constitutional duty.
Both sides claimed history was on their side.
Reid said it would be unprecedented to have a vacancy on the court for a year. In the modern era, the longest Supreme Court vacancy was 363 days after Abe Fortas resigned in May 1969.