The world stands on the brink of the abyss amid Russian nationalist demands for President Vladimir Putin to use nuclear weapons, Defence Minister Guido Crosetto said Thursday.     "It's a dramatic situation. I am convinced that in recent decades we have never reached the brink of the abyss as we have now," said Crosetto in his response to the Senate following his remarks on the Iran crisis.     "For years, Russian nationalists have been asking Putin to use tactical nuclear weapons against