On a gorgeous, warm autumnal afternoon, in a beautifully air-conditioned room, a man turned and delivered a slow and deliberate throat-slitting gesture.
It was directed at the media huddled together on a ‘riser’ at the back of a Donald Trump campaign rally.
It was alarming – and what was most remarkable of all was that no-one seemed in the slightest bit surprised.
It happened in Phoenix, Arizona, but the media has now become the pantomime villain at every Trump event. It is part of his narrative that this election is rigged.
A few minutes earlier in Phoenix, a man in a “Hillary for Prison” t-shirt had paced up and down the barriers between media and the public hurling vitriol towards the cameras.
Video of him apparently chanting “Jew-S-A” over that same barrier was later tweeted out by a reporter, earning him a denunciation from the Trump campaign.
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Also in the Phoenix crowd, another man yelled “media scum, liars” as he wandered past the same spot.
Another was removed by police and the Secret Service. He had stood, eyes closed, clutching something to his chest before glaring into the media enclosure.
Others turned the cameras on their phones on reporters, pointing out “culprits” to each other.
And this was even before Donald Trump had trotted out his crowd-pleasing standard about the media.
“They are the most dishonest, corrupt people,” he tells the crowd, who dutifully turn and boo, mostly with big grins on their faces. But not everyone.
It is in some ways a reflection of a very genuine and perhaps reasonable view that Trump is subject to a different standard of press scrutiny than Clinton – a belief that the liberal US media gives her a pass.
But it is an ugly manifestation of that frustration and it hardly endears the Trump cause to that very same media.
For weeks now, reporters have told of threats and abuse directed their way as people file out of Trump events.
They have expressed a real fear that the anger might boil over before this campaign is done.
Trump could choose not to turn the anger of thousands on a small group, penned in at the back of the room. But he doesn’t.
Most Trump supporters are unfailingly charming and polite and very keen to discuss their candidate’s merits.
They are often friendlier to foreign media than to domestic reporters.
But the mood and tone generated by some others should make us all worry about what might happen next.
:: Watch America Decides, a special programme on the US election at midnight on Monday.