Way too close to his brain for that to be a Roger Stone setup, unless he wants Trump dead, which he doesn't. This was real life, not William Tell shooting an apple off a head. Who would bet his life or his candidate's life on a 20-year old nonprofessional marksman hitting an ear instead of a head.
This showed really big lapses in Secret Service/local police protection. Like so many government agencies, the Secret Service seems inadequately staffed. The push to cut taxes and reduce the size of government doesn't account for the growth of the size and complexity of our society, economy, world geopolitical situation, technology, and problems in general. It is easy to revile government agencies but they are asked to do more and more with reduced resources and antique computer systems and software.
I also call nonsense on the claim upthread and by Rs that Biden and Ds criticizing Trump as a threat to Democracy caused the attempted assassination. Trump leads the world in inflammatory rhetoric and playing the victim. The shooter was a registered R with no evidence to date that this was a politically/ideologically-driven attack, although that may change with the shooter's electronic devices are examined. This could be a unhappy, mentally unstable, young male determined to make a name for himself, even if posthumously. John Lennon's assassin wanted to be linked to Lennon forever, had no grudge against him.