You'll have to be familiar with the general plot of the movie Diehard to understand this analogy:

In the movie Diehard there is a scene in which Hans Gruber (the main antagonist) encounters John McLane (Bruce Willis) on the upper levels of the tower. Hans pretends he was one of the hostages being held on the lower and has escaped. McLane appears to buy Gruber's story and eventually hands him a gun. When McLane turns his back, Gruber fires the gun and....surprise, Gruber! The gun wasn't loaded.

Gruber thought he was about to commit the crime but his action only served to exposed his true intent. Meanwhile McLane, though appearing vulnerable, knew he was never in any danger.

I hypothesize that the DS plotted a crime but a necessary element for the success of the crime was withheld from them without their knowledge. (Maybe the shooter was eliminated at the last moment or was a double agent, maybe the weapon provided was faulty. Maybe there weren't any bullets.)

If true, this would explain why the DS is now behaving as if they're covering up a crime while at the same time Trump behaved at the rally as if he weren't in danger (If you haven't already, watch the period of the event from when Trump ducks for cover behind the podium until he gets in the vehicle and ask yourself if his behavior is consistent with someone who has just been shot and is concerned about being targeted by a sniper.)

edit: this model would also explain why the outcome of this event that could have been overwhelmingly tragic was actually overwhelmingly positive (at least from a Great Awakening perspective). From the perspective of Trump's campaign there's really nothing better that could have happened, what fantastic optics! Plus the DS is thrown into defensive mode as the apparent crime is exposed and, more significant in my opinion, many of their tactics have been and will be exposed.

Note: I do assume there was a real professional sniper aiming at Trump (or that there was supposed to be). Here's why: if you rule out incompetence on the part of the SS then you're left with something like conspiracy to commit treason. I can't think of any possible in between. Nobody is going to involve themselves with this type of crime if the centerpiece of the crime (dead POTUS) is in the hands of a 20 year old kid without professional training. That would be like planning an Ocean's 11 style heist and employing a 16 year old kid with a driver's permit as the getaway driver. I don't believe any criminal would participate in something like that.