We find ourselves in an age of button diplomacy. Jeremy Corbyn, Justin Trudeau and Barack Obama – three very different politicians – are all fans of the unbuttoned top button. But what does the look tell us about their policies and their personalities?

An undone button is Corbyn’s sartorial trademark. Criticised for failing to properly tie his tie (thus, it’s said, hinting at an inability to compromise), the truth is actually more nuanced. “If you are standing up for the working classes, this look suggests that you are against the Man and with the people,” says Erynn Masi de Casanova, a sociologist and author of Buttoned Up: Clothing, Conformity, and White-Collar Masculinity. But it’s also crucial on the campaign trail, as it hints at the sort of connection politicians need – see Corbyn launching his manifesto in a suit, but also Corbyn interviewing the rapper JME, about first-time voters in an unbuttoned shirt.

“One is a uniform for the job and the other is down-to-earth and honest,” says Casanova. “It sends a good message, which is why Republicans often follow the same strategy.” Take Mitt Romney who often went tieless and unbuttoned as he campaigned for the White House in 2012.

Corbyn with JME. Photograph: i-D

Throughout his presidency, Obama’s approach to the undone button was perfectly struck, which made his appearance in Milan last week with two buttons undone something of a shock. Trudeau and Donald Trump, meanwhile, make a curious button neighbours. Proto-liberal Trudeau often goes unbuttoned. The Canadian PM knows he is a pin-up, “so this is intentional. His look says: ‘Judge me by my looks’,” explains Casanova. “It’s also a rejection of fashion being rejected, which is very modern. Suddenly, men are being judged for their clothes and they are not used to it, but Trudeau is ahead of the game.”

Which leads us to Trump, who conveys the opposite message. Buttoned right up with a too-long tie, his look belies a confidence that he is not being judged on his appearance. “Which is ironic,” says Casanova, “because he is trying to appeal to the working class – so his visual and verbal message are at odds.” It also, arguably, points towards the sort of narcissism that thinks his way – for example, Sellotaping his tie together – is the right way.

In many ways, button-undoing is an exercise of male privilege. “Business and politics are traditionally two social institutions dominated by men – there is no equivalent of the button for female politicians,” says Casanova. “In male-dominated fields, woman are also more scrutinised,” she says. As Susan Bordo explains in her 1999 book The Male Body: “I never dreamed that ‘equality’ would move in the direction of men worrying more about their looks rather than women worrying less.” Still, progress is progress.

So what of the others? Emmanuel Macron has adopted a more subtle look, buttoned-up with a discreet tie. It is both forgettable and the uniform of the establishment. Philip May, as our Flotus, went unbuttoned on The One Show last week in a bid to “visually pull back” from his wife’s status.

While no politician would forgo a suit, their approach to its accoutrements is loaded; see also the loosened tie, which implies the end of a long day’s work, and rolled-up shirt sleeves, which suggest you’re still at work. As for Trump, in his flapping suit, long tie and Sellotape, it’s probably best he stays away from buttons altogether.

• This article was amended on 17 May 2017 to correct the spelling of Emmanuel Macron’s first name.

