WASHINGTON (Reuters) - Liberal activists are urging U.S. Supreme Court Justice Anthony Kennedy, a conservative with whom they often disagree, to put off any thought of retirement, fearing President Donald Trump would replace him with a jurist further to the right. The liberal Democrats’ keep-Kennedy campaign, being pursued publicly and privately, reflects how powerless they have become against the Republican president when it comes to high court vacancies since the Senate in April reduced the vote tally needed to confirm a Supreme Court nomination to 51 from 60. It also shows how big the stakes are for both sides in any decision that Kennedy, who turns 81 in July, makes about his future on the court. If he were to retire, Trump would have a historic opportunity to recast the court in a more conservative posture, possibly for decades to come.  Some former Kennedy clerks have said he is thinking about retirement. He has declined to comment on his plans, despite requests from many media outlets including Reuters. Right now, Kennedy “is the most important man in America. He is the vote that swings the court on the most important cases that reach it,” said Elizabeth Wydra, president of the Constitutional Accountability Center, a left-leaning think tank. Nominated by Republican President Ronald Reagan in 1987 to a lifetime court seat, Kennedy has been a crucial swing vote on the nine-member court for more than a decade. On most issues, such as campaign finance and religious rights, he has voted with fellow conservatives. He also voted with the minority to strike down the 2010 Affordable Care Act, popularly known as Obamacare. But on gay rights and abortion, he has sided with the court’s four liberals. If he stays in his post, the court’s long-standing ideological balance will be preserved. If he quits, Trump could replace him with someone who tilts further right, giving conservatives a solid five-vote majority. Wydra and other liberals are lionizing Kennedy and his legacy in the media. Some are reaching out to former Kennedy clerks and others who know him, asking them to urge him not to retire, said Michele Jawando, a legal advocate at the Center for American Progress think tank in Washington. One former Kennedy clerk confirmed being asked to urge him to stay on and said other clerks had asked him to do so. Other clerks said they had not been approached by liberal activists. Since he took office in January, Trump’s only significant domestic policy achievement has been winning Senate confirmation of his nominee to the high court, Neil Gorsuch, a former Kennedy clerk. Gorsuch replaced a fellow conservative, Antonin Scalia, who died in February 2016. The Gorsuch confirmation did not shift the court’s ideological balance, but it did trigger a change in the Senate rules for considering Supreme Court nominees. To get Gorsuch confirmed, Republicans exercised the “nuclear option,” ending Democrats’ ability to use a procedural maneuver called a filibuster to block a final vote on a Supreme Court nominee. As a result, Republicans, with a 52-48 Senate majority, can now confirm any future nominee without Democratic support.  In another handicap, liberal groups said they lacked the money to sway public opinion via TV and online ads, unlike  conservative groups that had $10 million to back Gorsuch. In view of those disadvantages, People for the American Way, another liberal group, issued a report earlier this month outlining the impact of a Kennedy retirement, describing it as a “disaster for the rights of all Americans.” Liberals want in part to protect the 1973 Roe v. Wade ruling that legalized abortion. As a candidate, Trump said he would appoint court justices who would vote to overturn the decision. Perhaps seeking to reassure Kennedy that his legacy is in safe hands, Trump has consistently praised the justice. At Gorsuch’s swearing-in in April, Trump called Kennedy a “great man of outstanding accomplishment.” Trump and other Republicans have said they have heard rumors that Kennedy might retire, but have not publicly urged him to. The president has vowed to pick his next nominee the same way he chose Gorsuch, from a list of contenders he made public before the election. Among contenders viewed as possible Kennedy replacements are federal appeals court judges Raymond Kethledge and Thomas Hardiman, conservative lawyer and former Solicitor General Paul Clement and Brett Kavanaugh, a judge on the federal appeals court in Washington, according to a person with knowledge of the nomination process. 