Who funds Keir Starmer? That’s the question that Rebecca Long-Bailey and her campaign (echoed by Lisa Nandy) have been asking of the Labour leadership frontrunner.

Starmer has revealed some of his campaign donations, but the grace period in updating the register of members’ interests (which tracks the financial interests of members of the House of Commons) means that there may be more to come.

The attack line is a good one – in a vacuum. It’s a good way of trying to plan seeds of doubt about Starmer’s bona fides: is he really as leftwing as he has positioned himself in this contest – or can his “true” politics be divined from his donors? The problem is threefold: the first is that the overall trend in essentially all postal ballots, be they general elections, internal party contests, or the annual general meeting of the local wargaming society, is that most people vote almost immediately after they have got their ballot papers.

This is no time for a campaign to hit on a lucrative attack line because, however effective it is, the number of people who will be swayed by it is potentially too small to be decisive. But the bigger problem is that it runs contrary to the message that Long-Bailey’s campaign has been sending throughout the rest of the election.

One of the neglected subplots of this contest, if you ignore the tone of the respective candidates, and focus on the substance of what they’ve said, is that Long-Bailey has been the candidate most willing to exchange in explicit repudations of the party’s recent past. Long-Bailey was the only candidate willing to tell Labour members that regardless of how they felt about the topic, by 2024, the free movement of people will be a thing of the past in the Newsnight hustings. Her campaign is offering less of a tonal breach with the past than that of Nandy or Starmer, but more of a substantial policy breach. In addition, Long-Bailey has said that she will put Starmer in her shadow cabinet and, if offered, would take a job in his. It’s not coherent to both do that and to say that you are worried that there is something in his donation history that calls his politics into question.

The problem isn’t that the two are illogical: it’s that what you do is as important as sending a message as what you say. If Boris Johnson had, midway through his statement about the need for proper hygiene to help combat Covid-19, taken a massive sneeze without covering his mouth, then wiped his nose on his sleeve, he would have sent a much bigger message about how seriously we should take coronavirus (not very) than his words.

The number of Labour members who have seen Long-Bailey conduct a largely collegiate contest with Starmer, in which the expressed differences between the candidates have been few and far and far between, is very large. What that has done is communicate the idea that there is, in practice very little to fear about a Starmer leadership: and a late change of approach has to run against the overall impression that the campaign in question has helped to create. It’s akin to Yvette Cooper’s late pivot in the 2015 Labour leadership campaign from running against Jeremy Corbyn on a “Jeremy’s lovely, but he can’t win” to an explicit attack on the substance of his economic proposals. However effective or ineffective that change was, it was also far too late.

Just as it is hard to convince people you care about public sanitation while wiping a large gob of snot off with your sleeve, it is hard to convince people there is something worrying about one of the candidates when you have done so little to indicate it over the course of the contest.