WASHINGTON — Bernie Sanders scored three wins in Western caucus contests, giving a powerful psychological boost to his supporters but doing little to move him closer to securing the Democratic nomination. While results in Washington, Alaska and Hawaii barely dented Hillary Clinton’s significant delegate lead, Sanders’ wins on Saturday underscored her persistent vulnerabilities within her own party, particularly with young voters and activists who have been inspired by her rival’s unapologetically liberal message. In an interview with The Associated Press, Sanders cast his performance as part of a Western comeback, saying he expects to close the delegate gap with Clinton as the contest moves to the more liberal northeastern states, including her home state of New York.