Finally caught up with the thread … a few thoughts.
Technically, a shot of 130 yards with a decent off-the-shelf rifle is easy. I shoot groups of 5 within an inch diameter at 100 yards without being a top shot, but I have a very good optic. The fact that he (likely) didn’t use a scope, is baffling, as even a cheap one (USD 200) would increase the accuracy massively. Another factor against Crooks is that he would have been very nervous, thus degrading his aim.
The first three shots sound like they came well aimed, at a rate that a proficient shooter would be able to deliver. Shots 3-9 come at a very rapid rate, almost too fast for even a semi-automatic weapon. At least it would be not possible to re-acquire the target after the recoil. The recoil of a standard AR-15 rifle (chambered with 223 REM) is fairly light, and if you use a muzzle break, even lower. So if Crooks did shoot, I would say he delivered these shots with poor aim, after he heard the first three shots from another shooter. Basically just pulled the trigger as fast a she could without proper aim.
There are AR-15-STYLE weapons that are chambered with anything up to 308 caliber, so if it looks like an AR-15, it doesn’t necessarily mean it’s a 223 caliber.
Subsonic 223 REM is not feasible, in my opinion: The rounds are low grain (around 50 gr) and of very low impact force. This would be equal to a shot out of a .22LR rifle - good to shoot rabbits at 50-100 yards, but not much else. There are heavier caliber subsonic ammunitions like the .338 Whisper - but this is a 8.59mm bullet requiring a different rifle altogether. It is a huge bullet (nearly 40mm long!) and would be much easier to be captured on camera than the much smaller and a lot faster traveling 223 (around 3000 fps). And it would be near silent, if used with a suppressor. But these things (rifle and ammo) are hard to get.
I am not sure about the water tower. There is one video that is suggestive of someone hiding behind the trees on the walkway, but there are a lot of artifacts, although the timing is interesting. But it would be an awkward place to shoot. Ideally, you want to be prone for a precise shot, any other position degrades the aim. Also you have to have the rifle stably buttressed on something hard - that is not a shot you would want to take freehand. I guess you could maybe build a contraption that is fixed to the rails, dunno. And there is the issue of escape route, where your escape route is quite visible to anyone standing relatively close - the ladder down is quite exposed. If the scenario was a double shooter setup with Crooks as convenient patsy (and not in on it), you would make sure that the second shooter could slink off unnoticed.
Wind is always a factor that can change quite abruptly, but in regard to Crooks (under the premise that he gave out the shot that grazed Trump’s ear and that he effectively was using 223 REM), the wind drift of a typical load and bullet at 10 mph crosswind at 100 yards is only 1 inch (allegedly the wind was half of that) and 4 inches at 200 yards. I guess a combination of wind and Trumps change of head position could account for the miss.
For me at this stage the most likely scenario is a two shooter setup with Crooks as the patsy and a “backup” pro. I am not sure about the position of the second shooter, there are too much conflicting accounts (some say behind Trump, others to his left). As to why the pro failed, it may well come down to the sum of small “anomalies” that together stifled the pro (sort of the reverse of the old Swiss Cheese Theory) - which is another word for either damn luck or divine intervention (if there is anything like luck at all).
As to what is going to happen - I would think that another assassination attempt is unlikely. Even Trump dying of natural causes would bring an uproar that might spin out of control. Having said that, it seems to me that the event has blown over quite quickly - maybe the American people is still too comfortable to really rise up yet. So that means that one option is what others here have indicated as the C’s “program change” - let Trump win, then demolish the economy and pin it on Trump. The only other scenario that I can see is a state of emergency after a black swan event and a cancellation of the election.