DES MOINES, Iowa, Nov 14 (Reuters) - Friday's deadly Paris attacks will give a somber focus to the Democratic presidential debate on Saturday, putting front-runner Hillary Clinton and her two rivals on the spot over national security and their plans to fight Islamic State militants. CBS News, which is hosting the nationally televised two-hour debate, said it planned to press the candidates on how they would confront the evolving threat of terrorism in the aftermath of Friday night's bomb and gun rampage across Paris claimed by Islamic State, in which at least 127 people died.