We always knew that American presidential debates could make or break a candidate. It’s the primetime moment to shine or – in Joe Biden’s case – spectacularly evaporate. Poor Joe. To this day the thought of his incoherent mumbling still makes me wince with embarrassment.

I was there in the journalists’ watch room that night in Atlanta, and I can tell you that on multiple occasions the air fell silent. Reporters stared at each other in stunned disbelief while others blocked their ears.

One friend from a German broadcaster got up and walked out, slamming his fist on the table. “That’s it! It’s over!” he declared. “Biden is finished!” It seemed a tad dramatic at the time, but he had rightly called it within the first five minutes.

It was over for Joe Biden. He just didn’t know it yet.

Fast-forward to Philadelphia, and it was an altogether different feeling. Ripples of laughter filled the air as Kamala Harris got into her stride, relentlessly poking at Donald Trump, willing him to take the bait, which he invariably did: “People don’t go to her rallies!” he snapped belligerently at one point. But this, surely, was the soundbite of the night: “In Springfield, they’re eating the dogs,” Trump declared of the Haitian migrants who live there. “They’re eating the cats! They’re eating the pets!” Harris threw back her head and laughed.

The contrast could not have been clearer. Harris was as coherent as Biden was confused - as smooth as he was stupefied. But let’s be honest, the bar was astonishingly low. The mere serving up of words in the correct order was a step up. The relief in the room was palpable that we were witnessing an actual debate, with questions and answers.

As was the sense that Harris had won. This time the spin room belonged to the Democrats to boss. No more cowering in the corner, spouting lines for Biden: lines that, clearly, even they didn’t believe.

Harris had delivered for them a performance that had Gavin Newsom, the slick-haired Governor of California, giddy with excitement. Even his pearly white teeth appeared to sparkle that little bit brighter.

I was in the middle of interviewing Newsom when my producer alerted me that Trump himself had entered the building. The press pack immediately swarmed like excited bees to a drizzling honey pot. And there he was, holding court right in the centre – his favourite spot – with cameras craning for a glimpse and reporters yelling questions, willing the news gods to let theirs be the one that he would answer.

But on that night, the news gods chose to smile on your friend from Washington. After the Trump scrum was broken up, our keen-eyed cameraman, Ben, spotted the former president disappearing, like the Wizard of Oz, behind a giant black curtain and scurrying round the back.

We rightly guessed that he would pop up at Fox News, where we were waiting, ready to pounce.

“President Trump, did you win the debate tonight?” I asked as he was being mic’d up for his interview.

“I think we did great,” he told me.

“Did you feel you won?”

“I felt I won by a lot,” Trump said.

But had Harris rattled him, I asked.

“No, not at all”, came his reply.

“You seemed a bit rattled,” I suggested. And with a dismissive wave of the hand, he turned away.

It was vintage Trump: turn up to spin for yourself and declare that you won, even when most people believe you didn’t.

It was a TV spectacle, just like the debates themselves.

But is that all these debates are? Do they matter? For Biden they did. But for Trump, the reality TV president, seemingly less so.

The critics and pundits all had Harris as the clear winner. And yet, since the dust settled, recent polls have still put her neck-and-neck with Trump, or slightly ahead but within the margin of error.

Tune in this November as the American people write the next chapter of the presidential election show.

Siobhan Kennedy is Washington Correspondent at Channel 4 News.