After failing to land many blows during last month’s general election, the Conservative attack machine may have finally struck gold.

Guido reports that the Party’s video on Labour’s u-turn on student debt forgiveness has (as of two days ago) received more than 1.3 million views and 50,000 shares on Facebook.

The unravelling of this pledge, which appears to have been so pivotal to staving off disaster for Labour at the election, has been remarkable.

For an opposition party to be forced to abandon a very popular (but wildly irresponsible) spending promise before getting into office is unusual. Typically reality only sets in once in power, as the Liberal Democrats learned during their own tuition fees debacle.

It’s especially surprising as Labour are apparently deep in preparations for an early election. This is not how you normally treat a crucial group of voters if you believe the country may soon be going to the polls.

So why, only a month after taking 40 per cent of the vote on the back of a surge in youth turnout, might even Jeremy Corbyn’s allies such as John McDonnell be desperately trying to downgrade their pledge on student debt to an ‘ambition’?

The most obvious answer is that it blows Labour’s pretensions to fiscal responsibility out of the water, and they suspect they won’t be given a free pass on this by the Conservatives twice.

In the run-up to June, Labour placed great emphasis on their apparently ‘balanced’ tax and spending plans. We highlighted a few of the more egregious deceptions and items of muddled thinking, but luckily for Corbyn the Tories misplayed their strongest card by running on an uncosted manifesto themselves, making it hard to criticise Labour on the same grounds.

McDonnell set out these plans in Funding Britain’s Future, which identified £48.6 billion in new spending and, with eerie precision, £48.6 billion in tax rises to cover it.

But this plan makes no mention of forgiving student debt. Instead there is only “removing university tuition fees and restoring maintenance grants”, priced at a relatively humble £11.2 billion per annum. By contrast Angela Rayner, the Shadow Education Secretary, has suggested that the cost of forgiving student debt would be £100 billion or more.

It’s not hard to see why Labour’s cooler heads might see that as straightforwardly un-deliverable (and fear that it might spook the liberally-inclined wealthy voters who backed them over the Tories last month) and thus try to get their u-turn in from the safety of opposition as Nick Clegg wished to do.

Some of them may even realise that, as tuition fees are only repaid in line with earnings, such a policy is in effect a massive transfer of power to the better off, and that there are few less progressive ways to spend the education budget.

But that sort of nuance is not what Corbynism is about. His supporters believe he offers “straight-talking, honest politics”, and like the fact that he has spent his entire Parliamentary career criticising his party for trimming its socialist sails to the headwinds of political and economic reality.

Corbyn’s vague references to dealing with student debt, which did not feature in Labour’s actual election plan, had enormous cut through amongst voters who believe that he offers something different. But as the Liberal Democrats learned, the cost of over-promising is high: once disenchantment sets in, it sets in hard.