I guess I'm still left feeling extremely uneasy. I only see two options here. Either there was some big conspiracy to leave Trump unguarded or even take him out, or... it's just that easy for a 20 yr old goofball to get a rifle in an elevated position close enough to take pot shots at the president.
I'm still going with the third option of local LE unilaterally deciding to "take off early and leave" then getting locked out and otherwise fumbling their responsibilities. It happened at the worst possible time, just as the shooter was accessing his perch. JMO, the killer was lucky, local LE were highly unprofessional. Each outdoor event is unique and I think the odds caught up with them where someone outside SS wasn't doing their job.
As I've mentioned before, outdoor events are very risky. Dangerous things happen occasionally, but don't make the news. The SS just needs to say "no more", unless its a big state visit or similar event where SS alone has control of planning and security. WH events are also ok because the WH is the most secure location. JMO