US Supreme Court Justice Anthony Kennedy has announced he is retiring.
His decision will give President Donald Trump the chance to cement conservative control of the country's top court.
The 81-year-old said on Wednesday that he is stepping down after more than 30 years on the court.
A Republican appointee, he has held the key vote on such high-profile issues as abortion, affirmative action, gay rights, guns, campaign finance and voting rights.
Justice Kennedy said he has informed his colleagues and Mr Trump of his plans, and that his retirement will take effect at the end of July.
Without him, the court will be split between four liberal justices who were appointed by Democratic presidents and four conservatives who were named by Republicans.
Mr Trump's nominee is likely to give the conservatives a solid majority and will face a Senate process in which Republicans hold the slimmest majority, but Democrats cannot delay confirmation.
The president's first high court nominee, Justice Neil Gorsuch, was confirmed in April 2017.
Mr Trump is expected to name a nominee within weeks, setting in motion a process that could allow confirmation of a new justice by early August.
Mr Trump already has a list of 25 candidates - 24 judges and Utah senator Mike Lee - from which he will choose a nominee.
Prominent on that list are Judges Thomas Hardiman of Pennsylvania and William Pryor of Alabama, seriously considered for the seat eventually filled by Justice Gorsuch, and Judge Brett Kavanaugh, who serves on the federal appeals court in Washington, DC.