Everything I'm reading says the secret service saw and reported a weird, maladjusted white person acting like a creep at a Trump rally. They probably encounter thousands of guys exactly like that.
The real story is the goofy local cop who followed the assassin up to the roof but then completely chumped out after seeing the assassin had a gun.
The creep had a fucking range finder. The roof was not too dangerous to staff. They had eyes on the shooter for 90 minutes. They had civilians aware he was there with a gun for multiple minutes. The SS lied about various conditions. This just doesn't feel like mild incompetence.
Further, we know that FBI and other agencies have previously cultivated radicals and directed them towards acts of violence. Usually it ends in arrest, but the field guide, the practice, and the MO are all there.
Eh. It's really, really hard to stop one determined person who doesn't tell anyone what they're doing. To quote the RA - the SS has to get lucky every time, but a shooter only has to get lucky once. They have to stop every shooter.
It does illustrate something vital; the panopticon's surveillance is not perfect. It can't see everyone all the time. Individual actors can move through the gaps, or walk right in front of the cameras without being flagged.
Not sure if it matters but I have to keep reminding myself that the Secret Service detail assigned to former Presidents is much much smaller than what the sitting President gets and that people running for President don't get any Secret Service protection during the primary season.