Jeremy Corbyn would not be where he was without the monstrous missteps in the Bush-Blair “war on terror”. Labour members propelled this career outsider to the leadership in no small part in reaction to the bellicosity and authoritarianism that followed 9/11. By virtue of his mandate as well as his inclination, then, he feels not merely entitled but obliged to ask how things might be done differently in the wake of the Paris attacks.

Heaven knows it would have been useful to have had an opposition that asked awkward questions while rendition flights were winging their way to Guantánamo Bay, and the facts were being “fixed” to prepare for invading Iraq. There is today, as always after an attack, a danger that rash things will be done. After David Cameron again floated the idea of airstrikes in Syria today, Mr Corbyn asked a series of sensible questions in the House, many of them echoing the doubts of the cross-party foreign affairs committee. He invoked Barack Obama’s view that Isis grew out of the Iraq disaster, and pushed the prime minister on the vulnerability of police budgets in next week’s spending review.

All of this was perfectly reasonable – and yet almost nobody outside parliament will have heard a squeak of it, because it was overshadowed by Mr Corbyn having made a pretty monstrous misstep of his own. Questioned by the BBC on whether he would license the police to shoot dead the assailants amid a Paris-style attack, the Labour leader waffled about how he was not “happy with the shoot-to-kill policy in general”. It was not clear whether he was referring to the operational necessity of the police killing a terrorist in the heat of their crime, where this was the only available means to stop them killing more people, or whether instead he meant to indicate distaste for seeking out terror suspects in order to shoot them in the street, which is what “shoot to kill” meant in Northern Ireland. His use of the qualifier “in general” thickened the haze. In so far as the viewer at home was concerned, he was being asked a pressing, specific question.

In combating terrorism it is important, as Mr Corbyn would argue, to hold on to human rights. It is important, too, to bear in mind that police bullets can and do fell the innocent as well as the guilty, and do not threaten all innocents equally, but instead pose more of a risk to those whose skin colour or religious dress predisposes others to deem them a threat. In writing codes of police practice, all of this should rule out “shooting to kill” where there is any plausible alternative. But it does not – and cannot – rule it out when no other option exists.

His subsequent “clarification” to Labour’s national executive committee that he would in fact be happy with the police using proportionate force belatedly acknowledged that. But he of all people – already viewed suspiciously by many voters because of his controversial contacts – cannot afford to allow any room for doubt about his basic readiness to keep citizens safe.

A first instinct to talk about national security not as an aspiring prime minister but as a campaigner at a rally against police brutality is plainly bad news for Labour prospects. More than that, however, it retards efforts to persuade anybody not already converted to Mr Corbyn’s cause of the important argument about the need to build security upon something more than bullets and bombs. It is his duty to raise his game.