UK Prime Minister Keir Starmer faced mounting pressure to quit on Friday over his appointment of Peter Mandelson as envoy to Washington, after it emerged the veteran politician had failed security vetting. The affair has haunted Starmer for months amid growing anger over Mandelson’s 2024 nomination to the top diplomatic post despite his close ties to late US sex offender Jeffrey Epstein. Mandelson, a long-time insider with Starmer’s ruling Labour Party, has held multiple ministerial posts since...