With former President Donald Trump surviving the would-be assassination attempt at his rally in Pennsylvania last week, the focus has shifted to why the Secret Service was unable to defuse the situation before any shots were fired, given reporting indicates they were alerted beforehand of the gunman’s presence, and given claims by aides to Trump that the agents who tackled him to the ground actually put him in more danger. There’s a pretty simple explanation for it though, reporter Carol Leonnig told MSNBC’s Ayman Mohyeldin — a lack of preparedness that has triggered security breaches going ba…