According to Breaking Points, text messages from local law enforcement show they were aware and tracking the shooter and knew he was carrying a rangefinder, up to 1.5hrs before he shot Trump.
Local police photographed the suspect and suggested notifying SS Snipers to "look out" and sending in someone to "check it out".
The Secret Service and those up in the chain of command appear to have ignored the warnings and their requests.
Video here: https://youtu.be/6VIAGBfnNvQ
I wouldn't have anyone involved in the management of that operation organise a school crossing let alone the safety of an ex-President in the running to be the next President.