I don't think this has been corroborated. There are videos of a CS looking out to that side (which they were doing the whole time), but after shots are fired he repositions as if he wasn't looking at/couldn't see the target beforehand. The explanation I've heard for this is that USSS CSs are tasked with 3rd tier threats >300 yards away.

Also quoting their own article for the “source familiar with Trump’s security detail” isn't very compelling. The DISGRACED act is evidence of intent though so if they had better evidence of support denials it'd be pretty damning even to a moderate. Watching RFK Jr. get denied USSS detail for nearly year, after numerous real threats and his obvious familial history, is enough evidence for me that the administration is willing to politically assign protection though. That on top of all the primary rigging and age gaslighting gives a reasonably clear sketch of the administration's character imo which is consistent with this article's claim.