“Never interrupt your enemy when he is making a mistake,” Napoleon remarked. It is advice the Tories heeded this summer as they fell silent, content to allow Labour's infighting to monopolise the news agenda. But as the new political season begins, normal hostilities have resumed.

George Osborne yesterday warned that Jeremy Corbyn's nuclear unilateralism represented “a threat to our future national security and to our economic security”. That the Chancellor and likely next Conservative leader is attacking the frontrunner is evidence that he believes Corbyn has already won, or that his rebuke will only aid the left-winger (by confirming to the Labour selectorate that he's on the right side).

In today's Times, David Cameron joins the offensive, writing that “Listening to some of the anti-Nato, anti-American, profoundly anti-business and anti-enterprise debates is like Groundhog Day. Labour aren’t learning. They’re slaves to a failed dogma that has always left working people paying the price.” The Tories’ focus on Corbyn's foreign policy and defence stances shows that they regard these as his greatest weaknesses. By framing the left-winger as a threat to Britain's national security they believe they can quickly persuade the electorate to barricade the road to Downing Street.

But rather than merely exploiting Labour's perceived weaknesses, the Tories aim to neutralise their own. Aware that his party is still viewed as that of the privileged, Cameron continues his mission to rebrand it as “the true party of working people”. He vows that fines for non-payment of the new £9 “living wage” will be doubled to 200 per cent of upaid wages (up to a maximum of £20,000) and that bosses who fail to pay will be disqualifed as company directors for up to 15 years. Having originally opposed the introduction of the minimum wage, the Tories' aim is to show that they have unambiguously changed.

In response, Labour will point out that forthcoming cuts to in-work benefits will cost three million families an average of £1,000 a year. Tax cuts and a higher minimum wage will not compensate the many losers. The test for Corbyn will be whether this message is heard over the cacophony of attacks on him. As Ed Miliband learned to his cost, leaders of the opposition have only a narrow window within which to define themselves. Corbyn will have to use his time wisely.