Several major questions have emerged for the US Secret Service to answer in the aftermath of the shooting of Donald Trump at a rally in Pennsylvania. The FBI has taken on the role of lead investigator into the incident, during which one person was killed and two others critically injured - while Trump was wounded in the ear. As the US demands answers, the Secret Service says it is working to discover "what happened, how it happened, and how we can prevent an incident like this from ever taking place again". Its chief, Kimberly Cheatle, has been summoned to testify...