By Trevor Hunnicutt and Jarrett Renshaw WASHINGTON (Reuters) – U.S. President Joe Biden, his aides and Western allies are scrambling to explain his remark that Russian leader Vladimir Putin could not remain in power because they do not want to escalate conflict between Washington and Moscow, officials said. The nine-word line, at the end of a 27-minute speech in Warsaw on Saturday, has distracted from what some observers regard as the best piece of rhetoric of Biden’s presidency. It made foreign allies uneasy at the end of an otherwise successful trip aimed at uniting allies against Russia, an…