Sometimes sounds can be deceptive. A car backfiring can make you jump; a firework can make you flinch; but as soon as we heard the gunfire at the Butler Farm showgrounds shortly after 6pm on Saturday evening, we all knew straight away that these were gunshots, and there were lots of them.

Donald Trump was mid-way through a sentence as the shots rang out. He grabbed his ear before dropping to the ground and being smothered by Secret Service agents.

We didn’t know it at the time, but the gunman was perhaps 150m away from where we stood, lying flat on the roof of a shed and firing at least six rounds using an AR-15 rifle at the former president and terrifed spectators.

I was about to go on air, with radio colleagues from the BBC World Service waiting on the end of a line. Instead all three of us in my team – me, producer Iona Hampson and cameraman Sam Beattie – went to the ground, using our car as some kind of shelter, the only shelter we had.

We had no idea where the shooting was coming from; how many shooters there were; and how long it would go on for. Frankly it was terrifying.

As we lay on the ground, Sam turned on his camera and I tried to give my first impressions of what was happening. In that moment, we had no more concrete information than that about six minutes into Donald Trump’s speech, the shooting had begun.

As I listened I could hear screams from the crowd but I could no longer hear the former president speaking. Was he hit, was he dead? All these thoughts flash through your mind.

When we felt the shooting was over, Iona picked me up off the ground and we went live on television as shocked members of the crowd poured out of the exits. The range of emotions we encountered was immense, as Iona persuaded terrified spectators to come and talk to me live on television.

Many were understandably frightened; many were dazed and bewildered; some were angry, very angry.

One witness, a man named Greg, said he had seen the gunman “bear-crawling” onto the roof of the shed minutes before the chaos began and had been frantically trying to point him out to police and the Secret Service.

Another man – and I can understand this – was furious that we were broadcasting; he put himself between me and Sam yelling at me to stop. I laid my hand as gently as I could on his arm and explained to him while we were on air that it was important people knew what had just happened; the public, I said, had to know.

Eventually, as I pleaded with him, he relented – still unhappy and still fuming, rightly so, at what he’d just experienced.

Others expressed their anger in more political ways.

One man approached me and simply said: “They shot first. This is [expletive] war.”

Another just yelled “civil war” as he passed behind me.

And a few minutes later a huge electronic billboard appeared on the side of a truck – Donald Trump’s face framed in a target – the words simply read “Democrats attempted assassination – President Trump”.

It sent a shiver right up my spine – and the horror of the potential consequences of this act started to sink in.

But amid the fear and anger, there was profound sorrow. People who were loyal Trump supporters, committed gun owners, wondered out loud to me about the way America was going. It was as if they could no longer recognise the country they lived in – as if everything had become strange and foreign.

Devin, a local farmer, was there with his son Kolbie. It was their first ever political rally – Kolbie, just 14, still not old enough to vote.

But Kolbie’s first experience of the rawness of democracy was to see two wounded people loaded onto stretchers and rushed off to ambulances. It’s hard not to believe that those images of muzzle flashes he witnessed from the Secret Service snipers who took down the gunman won’t stay with him for the rest of his life.

I’ve covered at least half a dozen shootings in my ten years as a correspondent in the US – but always the immediate aftermath – never have I been present until now when someone actually pulled the trigger.

I don’t want to experience it again, and in this gun-loving country, even those committed to their handguns and rifles in this rural part of Western Pennsylvania seemed sickened and worried about the randomness of the violence they witnessed in late-afternoon sunshine as they wondered whether their political hero was still alive.

But what happened in Butler goes much wider than arguments over gun control.

America has been spiralling towards this moment for years – a political culture that is not just adversarial but downright poisonous. People here – or should I say some people here – find it easy to hate their political opponents – it’s visceral; it’s become part of the nation’s DNA to hate.

And it’s not just political. You can see it in the divisions between the coasts and the centre. Between the north and the south; between the cities and rural America – everything being defined in terms of not being something or someone else.

Moments in history can only really be judged in retrospect. But I’ll take a guess that last night will go down as one of those moments. The question for the leaders of public opinion in this country is what will they now choose to do – to inflame or to calm. To further divide or to reunite.

As an outsider but someone who truly loves this nation, I’m not hopeful.