There’s a reason why politicians pose with babies, a reason why the oldest photo-op in the campaign manager’s handbook is of a candidate holding, embracing or kissing a tiny child. There is no faster way of humanising a politician, demonstrating that he or she is a caring, sensitive and loving human being than having them show tenderness towards an infant. Besides, everyone smiles when they see a baby – and some of that good feeling is bound to rub off on the person we see with them. We can’t help ourselves.

A prime, if subtle, example came when Michelle Obama sought to introduce her husband to the Democratic convention that nominated him for the presidency in 2008. Barack, she said, is “the same man who drove me and our new baby daughter home from the hospital 10 years ago this summer, inching along at a snail’s pace, peering anxiously at us in the rearview mirror, feeling the whole weight of her future in his hands ...”

Clearly that was the one bit of Michelle Obama’s 2008 speech Team Trump didn’t, er, study closely. For we can now add to the long list of political rules Trump has broken – don’t insult disabled people, don’t insult war heroes, don’t insult the parents of a fallen soldier – one more. Don’t be mean to babies.

At a rally in Virginia on Tuesday, a baby started crying. At first the Republican nominee affected to indulge the interruption. “Don’t worry about that baby,” he said. “I love babies ... I hear that baby crying and I like it. I like it. What a baby, what a beautiful baby. Don’t worry, don’t worry ... It’s young and beautiful and healthy and that’s what we want, OK.”

But a few minutes later, when the bawling had not stopped, Trump lost patience. “Actually I was only kidding,” he said. “You can get the baby out of here.” Of the mother misguided enough to have been reassured by his earlier words, he said, “I think she believed me that I love having a baby crying while I’m speaking. That’s OK. People don’t understand.”

On one level, this is no more than yet another, relatively minor example of Trump doing something political convention would deem unacceptable – signalling to his most committed supporters that he’s a rule-breaker and a maverick and therefore someone they can trust to smash the system they despise. For a certain kind of Trump devotee, there’s nothing he can do that will repel them: as he himself has noted, he could stand on Fifth Avenue shooting people and they’d still vote for him.

For others, though, it might play out differently. The most obvious group is women, where Trump lags far, far behind Hillary Clinton: 34% to 57% according to the latest CNN survey. Pollsters have identified a particular segment of that group as crucial in this election: white, college-educated women. They can often lean towards the Republicans, but are currently recoiling from Trump. This latest episode is unlikely to endear him further.

The world saw a grieving mother. Donald Trump saw a Muslim | Amana Fontanella-Khan Read more

Not least because it has acted as a reminder of Trump’s curious attitude to young children. A lawyer has testified that in 2011, when she asked for a break during a legal proceeding involving Donald Trump so that she could pump breast milk for her baby, he turned to her red-faced and screamed, “You’re disgusting, you’re disgusting.”

More telling still is an episode the Daily Beast rightly describes as “creepy”. In 1994, his wife Marla had just given birth to a daughter, Tiffany, and Trump gave an interview about the new arrival. “Well, I think that she’s got a lot of Marla,” he said. “She’s a really beautiful baby, and she’s got Marla’s legs. We don’t know whether she’s got this part yet, but time will tell.” As Trump said the words “this part”, he gestured toward his chest.

There’s a reason why even respected political commentators now state baldly that Trump has some kind of personality disorder. There seems to be something missing. His attacks on the Khan family – whose son was killed in combat – were faulted above all for their complete lack of basic human empathy. In Virginia on Tuesday, he couldn’t show empathy for a mother struggling with a crying baby, let alone the baby itself.

They say there’s no hiding from the long, intense scrutiny of a presidential campaign. It reveals character. It finds you out. In ways large and small, the true nature of Trump is being revealed – and it’s not pretty.