DUBAI, United Arab Emirates — Qatar has hired a Washington influence firm founded by former top campaign aides to President Trump and another specialized in digging up dirt on U.S. politicians, signaling it wants to challenge Saudi Arabia’s huge lobbying efforts in America’s capital amid a diplomatic dispute among Arab nations. Qatar, in the midst of building stadiums for the 2022 FIFA World Cup, isn’t afraid to spend its money. Since the crisis began, Qatar paid $2.5 million to the law firm of former U.S.