WASHINGTON (Reuters) - A Republican-backed Senate rule change expected on Thursday could make it more likely that presidents will pick ideologically extreme U.S. Supreme Court nominees with little incentive to choose centrist justices, experts said. With a deep partisan divide in Washington, Democrats are using a procedural tactic called a filibuster to try to block confirmation of President Donald Trump’s Supreme Court nominee Neil Gorsuch in the Republican-led Senate. Majority Leader Mitch McConnell has threatened to change long-standing rules in the 100-seat Senate if the Democrats succeed with the filibuster in order to prohibit the tactic against Supreme Court nominees. That would mean such nominees could be confirmed by a simple majority rather than needing to first muster a 60-vote super-majority. Experts said the rule change, called the “nuclear option,” could produce an ever-more ideologically polarized Supreme Court. Over the years with the Senate narrowly divided, the filibuster rule has meant that presidents have needed to make appointments who could win at least a few votes from the other party. For the court, the prospect of a filibuster has shaped the way presidents pick nominees, said Stephen Wermiel, a Supreme Court scholar at the American University Washington College of Law. “Although it has not been widely used, the idea that it was there as a deterrent to presidents appointing justices who might be considered extreme has been a significant factor,” Wermiel said.  Republican Senator John McCain, a defender of Senate traditions, warned of the consequences of the rule change, though he said he would reluctantly support the move. “We will see more and more nominees from the extremes of both left and right,” McCain said. “I do not see how that will ensure a fair and impartial judiciary. In fact, I think the opposite will be true, and Americans will no longer be confident of equal protection under the law.” Republican Senator Lindsay Graham said Supreme Court  nominees “are going to be more ideological, not less” with the rule change, which he warily supported. The nuclear option would erase “the last shred of bipartisanship in the Senate confirmation process,” said Senate Democratic leader Chuck Schumer, who led the filibuster against Gorsuch. Elimination of the filibuster for Supreme Court nominees could matter most with the next vacancy on the nine-seat court after Gorsuch, who was nominated by Trump to replace Justice Antonin Scalia, who died last year. Three current justices are 78 or older: liberal Ruth Bader Ginsburg is 84; conservative Anthony Kennedy, who sometimes sides with the court’s liberals in big cases, is 80; and liberal Stephen Breyer is 78. Having more justices who are ideologically extreme would make compromise among them harder and lead to rulings the public may view as based more on a political agenda than the law, said University of Massachusetts, Amherst political science professor Paul Collins, co-author of a book on Supreme Court confirmation hearings.  If confirmed as expected on Friday, Gorsuch would restore the court’s 5-4 conservative majority. Overturning the landmark 1973 Roe v. Wade ruling that legalized abortion nationwide may become more likely if there is no filibuster to moderate the choice of future court nominees, Wermiel said. Without a filibuster, a future Democratic president with a Democratic-led Senate could feel free to name a justice from the dogmatic left. The result would be a court even more polarized than the current one already is perceived to be, said Brookings Institution think tank expert Russell Wheeler said. “An ideologically-driven administration would eschew middle-of-the-road judges,” Wheeler said. “They would stack the court with ideological soulmates.” Trump advisor Leonard Leo said the best way to avoid extreme nominees is through the electoral process. Trump made it clear during the 2016 presidential campaign he would pick from a list of potential Supreme Court nominees that he made public, and the voters elected Trump, Leo said.  “People knew or should have known what they were getting when he was elected president,” Leo said.  
'Nuclear option' fallout? More extreme U.S. justices, experts say