On retrospect, in a country with so many guns like ours, maybe an outside venue was not wise.
But, on the other hand, outside it is possible for more interested people to participate, just as the people who alerted to the shooter did- they could just come informally with a picnic, and that would not be possible if it were indoors.
I'm sure SS alerted the campaign about the limits of a realistic perimeter.
It still seems like that rooftop would have been a good place for local LE to put their lead person- with a good view of the area. On retrospect, it also would have been a good place for the owner/lease to put private security just to prevent having spectators climb there dangerously. Who needs to deal with broken wrists and legs that could follow a group deciding to get a closer look from there.
But overall, I'm sure the campaign was aware of the benefits of the venue and the risks.
Even in rural USA, even with candidates heavily influenced by the NRA, it is more likely that a shooting not happen at a rally. The venue was chosen by the campaign- it was accessible and had many pluses. SS can give a safety assessment but they can't tell the campaign to reject a venue. The unlikely scenario that an assassin would come on the scene and fire shots did not dictate decision-making.
MOO