What makes a leader, and what is leadership? We are told every day that Jeremy Corbyn is not a leader, from Hilary Benn’s “He’s a good and decent man, but he’s not a leader” to the Daily Mail saying Corbyn “is the worst Labour leader in history”. But in spite of the relentless Corbyn-bashing, beyond the ability to win elections (Owen Smith: seriously?) there has been little discussion of what a leader, or leadership, means.

The adjective that sidles up most insistently to “leader” tends to be “strong”. For a strong leader is the thing to be. Margaret Thatcher was a strong leader. Tony Blair was a strong leader. David Cameron? He had pretensions in that direction. Theresa May’s performances at PMQs suggest she believes she too belongs in the strong leader club, and that condescension and archness are the way to achieve it, though her bid for membership took a turn for the worse this week when Corbyn challenged her on grammar schools.

Not all of us, however, are quite so in thrall to politicians who take voice coaching, visit bespoke tailors, employ image groomers, holiday with media moguls, or jettison past commitments (Blair’s unilateralism, for instance) when these things start to get in the way of a smooth ascent; and – to prove they are really strong, that they have the guts to take the really difficult decisions – bomb or invade some of the poorest countries on Earth.

On Wednesday a foreign affairs committee chaired by the Conservative MP Crispin Blunt delivered its excoriating verdict on David Cameron’s Libyan adventure. Few people will rush to Cameron’s defence. Yet the former prime minister might be forgiven for feeling a pang of irritation at the committee’s uncompromising verdict. In March 2011, when Cameron went to the Commons to propose bombing Libya, no fewer than 557 MPs voted with him. Just 13 voted against.

Those 13, just in case anyone is interested? They did not include Crispin Blunt. They did not include Theresa May. They did not include Owen Smith, Corbyn’s rival for the Labour leadership or Angela Eagle, who kicked off the leadership challenge (she abstained). But they did include Jeremy Corbyn and John McDonnell. That’s what many of us call leadership.

Just last year Cameron was at it again, sombrely assuring the country that the deployment of Britain’s air power over Syria was essential for the defeat of Islamic State. It showed how little MPs had learned from the catastrophic interventions in Afghanistan, Iraq and Libya that the government was able to muster another majority. But it did. Among those who opposed, amid the familiar howls and insults and questions about their patriotism, were Jeremy Corbyn and John McDonnell.

Spooling backwards to March 2003, and the eve of the invasion of Iraq, when Blair told the house that Saddam Hussein’s weapons on mass destruction not only justified invasion but necessitated it as an urgent act of self-preservation, 412 MPs voted for the war, 149 against. Leading up to the vote, the government whips subjected Labour MPs to every kind of inducement and coercion – much of it highly unpleasant – in an effort to get them to support invasion. Those who held out were branded appeasers and cowards. Among them? No prizes for guessing: Jeremy Corbyn and John McDonnell.

‘When he had a full head of hair and weighed a pound or two less, he was out on the streets marching (and being arrested) for the end of apartheid in South Africa and the release of Nelson Mandela, who was then branded a terrorist.’ Photograph: Greg English/AP

When it comes to foreign military intervention, do I look to strong leaders or to someone who has, over 30 years in parliament, consistently shown that he makes the right call? Those MPs who now shake their heads in dismay at the utter calamity of Cameron’s bombing of Libya and Blair’s invasion of Iraq had the chance to make the right call.

But they didn’t. They failed. At the time when it really mattered, when the vote was before the House, when the issue was live and front and centre, they failed. Their judgment, their principles, their ability to stand their ground – they all went missing.

It is all very well to say, years after the event, that you believed the prime minister when he said that Saddam had weapons of mass destruction, or that bombing Gaddafi would bring peace and democracy to Libya. But what counts is what you do in the moment. What counts is where your vote goes. That’s when you get your chance to make the right decision.

Time after time, the Labour party’s worst leader in history has called it right. When he had a full head of hair and weighed a pound or two less, he was out on the streets marching (and being arrested) for the end of apartheid in South Africa and the release of Nelson Mandela, who was then branded a terrorist. I know because, like thousands of others, I saw him there. We didn’t see the iron lady, Margaret Thatcher. And maybe I wasn’t looking hard enough, but I didn’t see Tony Blair either.

When the scandal of systematic miscarriages of justice involving innocent Irishmen and women was at its height in the 1980s, desperate families approached senior members of the Labour opposition for help in reopening the cases. They were rebuffed. Anti-Irish sentiment was rife, and there were no votes for responsible politicians in helping Irish prisoners against the police and judiciary. Who took up their cases? Jeremy Corbyn and John McDonnell (not forgetting Chris Mullin’s powerful work on behalf of the Birmingham Six). Corbyn and McDonnell had the courage – and it took courage back then – to campaign and organise. But that’s what leaders do.

On ID cards, on extended detentions, on equal pay and gender quality, on protection for workers and trade union rights, on anti-racism initiatives, on tax avoidance by the super rich, on the bedroom tax, on the recent welfare reform bill (Owen Smith? He abstained), on PFI – a massive, shameless scam perpetrated by financial institutions already as rich as Croesus, aided and abetted by government, that has brought the NHS to its knees – Corbyn and McDonnell called it right.

Give me this kind of leader anytime.