Embattled Secret Service head Kimberly Cheatle has revealed the fateful reason why her agency failed to position an agent on top of the building that a gunman used to carry out an assassination attempt on Donald Trump. Cheatle, who is already facing calls to resign over what some lawmakers are calling a massive security failure, said Secret Service officials planning security for Trump's rally in Butler, Pennsylvania considered the warehouse about 150 yards away from where Trump spoke to be a risky position for stationing an agent. 'That building in particular has a sloped roof at its highest point. And...