The Secret Service apparently had enough kit in place to shoot the guy after the fact. If they could see him well enough to do that, they ought to have been able to get a peek at him before he started taking pot-shots at Trump.
Having said that, the building in question was outside the Secret Service’s perimeter and hence the responsibility of the local police, so at the very least there were bound to be communication issues.
The problem with the former, as far as I’m concerned, is that the Secret Service, for all its faults, ought to have been able to find somebody whose marksmanship skills extended to actually hitting vital parts of Trump (not exactly a small target) with at least one out of eight shots at 100 metres or so (not exactly a huge distance, for an AR-15-style rifle), as opposed to a random juvenile gun nut who, we’re told, didn’t just not make his high school’s rifle team on the first attempt but was asked not to try again.
OTOH, perhaps both alternatives are true at the same time 
