first, the shooter was a conservative apparently really into guns. quit trying to make this into a liberal thing. eat your own vegetables. once the facts began getting investigated i began thinking "political violence" needed to be stowed as it ignores the "hinckley"/"fromme" potential. aren't you the "some of these shooters are crazy" folks?
second, the shooter has been described as someone who tried out for the school rifle team and was cut, didn't even make JV due to safety and accuracy concerns. so factor that into your "competent shooter would have....." analysis.
third, in terms of "competent shooter," my understanding is locals saw the shooter, at least one local PD was on the roof confronting the suspect, who turned around at the PD, who dropped to the roof, then shooter turned back to the target for a rushed shot before either PD or secret service can get him. he gets off the rushed shot but wings his target. he's no longer taking a calm shot. secret service then snipes him before he can settle and reaim.
fourth, i think secret service botched this and/or is insufficiently integrated with local PD to have full situational awareness. all i have ever heard is how they take over some wide radius and block everything off. then have snipers looking for precisely this scenario. how do you get on a nearby rooftop unseen? to me it's maybe this is the first time the contingency ever happened. so you're a counter-sniper but 99.99% of the time it's nothing doing. like a cop who has been on the streets for 15 years but never fired their gun off a target range. maybe takes a second to activate their training. or they freeze.
i mean, as a soccer player, having a chance on goal shouldn't be any different than warmup practice, place your chance in the edges of the goal, and yet only so many players can chill out and do the skills like it's the case. a lot of folks tend to throw power behind it and whack it way over. there's practice and there's real.
last, the "official duties" immunity decision is a horribly thought out joke that only encourages this sort of conspiracy thinking. by this argument bribery is always an official act because you usually have the authority to do x that you are being paid for. even if the constitution lists bribery as an impeachable offence. running for office is not an official duty -- does RFK get immunity? trump is asking for immunity for stuff he did running for an office he lost. how is that part of his existing job. in some states it's a crime to electioneer from your office or your office phone. we have the hatch act federally where you're not supposed to electioneer on official business.
ironically, having sent scotus the immunity issue what that got dismissed on was something else.