The possibility that the attack was staged as a false flag occurred to me, too, in the early minutes after the event when basic facts were yet to be established and it was just being reported as "Trump whisked off stage after shots fired". It's sad to say, but it's the sort of thing you can't put past a fundamentally dishonest, TV image obsessed person like Trump, the propagandists around him, and his cult-like followers who'll, I dunno, storm a federal government building intending to kidnap and/or kill politicians they don't like and any uniformed police officers who happen to stand in their way. OTOH, as soon as I saw the photograph with traces of blood on his face, I knew the attack was real.