Herman Cain, the pizza mogul who would be US President, looked in danger of becoming the latest shooting star of the Republican field to fall back to earth, as a poll yesterday showed his inept response to sexual harassment claims had dented his credibility with potential voters.  While Mr Cain's campaign had initially tried to dismiss the allegations as a media confection and supporters called it a witch-hunt with potentially racist motives, the scandal has continued to dominate the Republican race and rival candidates piled in over the weekend to demand that Mr Cain puts "all the facts on the table". It emerged last week that the National Restaurant association paid a legal settlement to an employee who made a written complaint about Mr Cain's behaviour towards her wh