GENEVA - The UN High Commissioner for Human Rights launched a thinly veiled attack on US Republican presidential front-runner Donald Trump and other presidential hopefuls on Friday, in a speech entitled 'The road to violence' in Cleveland, Ohio. 'Bigotry is not proof of strong leadership,' Zeid Ra'ad al Hussein said, after criticizing 'a front-running candidate to be President of this country' for advocating the use of torture and multiple candidates for supporting surveillance of Muslims.