How Was Trump's Would-Be Assassin Thomas Crooks Allowed to Get So Close?

Questions are being raised about the security lapse that put Donald Trump in the line of fire over the weekend. Thomas Crooks apparently climbed on to the roof of a building owned by a glass manufacturing company. A local police officer was alerted to the presence of a potential sniper, and he climbed to the roof to confront Crooks. Crooks pointed his rifle at the officer, who either fell or backed off, moments before the first shots were fired.