"Staged" could mean:

1. They planned to let the guy get a gun close then nab him without shooting, but fucked up.
2. They planned to let a bad shot take a shot and then execute him.
3. They had a patsy on the roof and a real shooter elsewhere, who planned to either miss (and succeeded) or hit (and fucked up).

All of which would involve a real bullet actually killing someone, just not Trump.