WASHINGTON — Democrats could confirm a successor to Justice Stephen G. Breyer without any Republican support under Senate rules that shield a Supreme Court nomination from a filibuster, but would have to hold their bare majority together to do so.
The announcement of Justice Breyer’s imminent retirement on Wednesday set off a sprint by top Democrats to prepare for a coming confirmation fight over President Biden’s nominee to succeed him. It also prompted a collective sigh of relief from the party and its progressive allies, who had worried that a Senate takeover by Republicans in the coming midterm elections could block the president from filling any vacancies.
Senator Chuck Schumer, Democrat of New York and the majority leader, promised on Wednesday that Mr. Biden’s “nominee will receive a prompt hearing in the Senate Judiciary Committee, and will be considered and confirmed by the full United States Senate with all deliberate speed.”
Changes in Senate rules in 2013 and 2017 mean that a nominee can move forward and be confirmed with a simple majority. With the Senate split 50-50, Vice President Kamala Harris would be able to break a tie over any nominee, giving Democrats the upper hand as long as all 50 of the members who vote with them rally behind whomever the president chooses.
While Senate Democrats have split over some policy issues, they have been very supportive of the judicial candidates the Biden administration has put forward.
Democrats quickly called on Mr. Biden to follow through on his promise to nominate the first Black woman to the court.
“I trust President Biden to move forward an exceptional nominee who will uphold all American’s rights and liberties — including protecting voting rights and reproductive rights,” said Senator Patty Murray of Washington, the No. 3 Democrat. “I am ready to move as quickly as possible to consider and confirm a highly qualified nominee who will break barriers and make history as the first Black woman on the Supreme Court of the United States.”
Mr. Biden has been highly successful so far in nominating and confirming federal judges, but his nominees have so far drawn few Republican supporters.
But with Senate Republicans in the minority, they lack the power to erect the kind of blockade they did when they controlled the chamber in 2016, preventing President Barack Obama from even getting a hearing for his nominee to the court, Merrick B. Garland.
In a message clearly intended to rally conservative support ahead of the midterm elections, Senator Lindsey Graham, Republican of South Carolina, noted on Wednesday that Democrats “have the power to replace Justice Breyer in 2022 without one Republican vote in support.” He added, “Elections have consequences.”
The Judiciary Committee has been anticipating a potential Supreme Court showdown since Democrats took over the Senate in January and Senator Richard J. Durbin, Democrat of Illinois, became the committee’s new chairman. Though he has long experience on the panel, this would be the first time he would oversee a Supreme Court confirmation.
If any Senate Democrat broke from the party on the nomination — as Senators Joe Manchin III of West Virginia and Kyrsten Sinema of Arizona often have on major policy issues in the Biden era — it could endanger Mr. Biden’s pick and provide cover for Republicans to be in opposition as well.
Catie Edmondson contributed reporting.