Which Labour leadership candidate has most in common with Bernie Sanders? Few of the Democratic presidential candidate’s admirers on the British left would say the answer was Keir Starmer. Yet that is precisely the comparison the favourite for the Labour leadership wants 580,000 members and supporters to make as they begin to cast their ballots this week. In an implicit rebuke to Lisa Nandy and Rebecca Long-Bailey, Starmer says he is not just in the business of uniting a fractured party at Westminster, but broadening its base in the country. Cultivating new support across class and ethnic divides has put Sanders on the road to the Democratic nomination, and Starmer believes that the same approach can put Labour back on the path to power: keep left, rebuild a diverse coalition of voters, and look beyond the red wall.

Labour leadership: Keir Starmer on course to win in first round – poll Read more

Unsurprisingly, Rebecca Long-Bailey’s camp does not agree. With voting under way, the shadow business secretary’s supporters on the left are doing all they can to convince members that Starmer is precisely the opposite sort of politician to Sanders and, by implication, Jeremy Corbyn. Last week, Ian Lavery, the Labour chairman, was deployed by Long-Bailey’s stuttering campaign to needle Starmer in the pages of the Sunday Times. He posed a simple question: who funds you? “All candidates should be comfortable disclosing the source of campaign donations prior to the ballot papers being sent out so that members can cast their votes in full knowledge of their candidate’s funding,” he said. Speaking at the Oxford Union last night, Unite’s Len McCluskey warned Starmer that “financiers lurking in the shadows” had no place in the Labour party.

Though Lavery did not mention Starmer by name, he did not need to: it isn’t so much a dogwhistle as a tuba. Unlike Sanders, both of whose leadership runs at the White House have been powered by small individual donations, the likes of Lavery want members to believe that Starmer is the candidate of the big money donors who largely abandoned Labour during the Corbyn years. On Tuesday, Long-Bailey went even further, releasing details of every one of her donations above £1,500. Though he insists that his donations will be disclosed “in the usual way”, in the parliamentary register of interests due to be published next Monday, Starmer has ignored calls from the Corbynite left to follow suit immediately. Long-Bailey’s allies believe they have found the smoking gun. As one supportive shadow cabinet minister puts it: “What does Keir have to hide?” The answer, as far as they are concerned, is a funding model and political modus operandi that is much more Blair than Bernie.

Other Long-Bailey supporters have been even more explicit. Novara Media paint Starmer as the inheritor of a “shifty, evasive” Labour right tradition. As ballots went out on Monday, meanwhile, the Fire Brigades Union released a video that reminded members in no uncertain terms of his resignation from the front bench at the height of the coup against Corbyn in 2016. Unite’s Len McCluskey, who was more than happy to make life difficult for Ed Miliband, the last Labour leader whose politics diverged from his own, has said only Long-Bailey can be trusted to guard Labour’s values.

Yet anyone watching the woman herself on stage with Starmer at a hustings could be forgiven for assuming a case of mistaken identity: their clashes have been comradely and convivial, the disagreements confined to policy, the personal relationship clearly one of genuine warmth. Each says they will appoint the other to their shadow cabinet. And while Long-Bailey has gone further than Starmer in throwing red meat to the Corbynite left on the issues that animate it most, like mandatory reselection of MPs, there has been very little substantive disagreement on the big question of where the party goes next. Give or take differences of style and emphasis, both have the same answer: travel in the same direction as Jeremy Corbyn (when it comes to domestic policy, at least).

The new Labour leader will try to unite the party – but around what? | Rafael Behr Read more

That’s precisely why all the available evidence suggests Starmer is going to win, and win relatively easily. Long-Bailey was earmarked as the candidate of continuity Corbynism years before this leadership election was even called, but it is Starmer who has really owned that mantle. Labour members did not vote for Corbyn in overwhelming numbers twice because they were all entirely at one with him ideologically, but because he was the best at communicating the values that the selectorate cared most about, chief among them full-throated opposition to austerity.

Yet that isn’t to say Starmer has nothing to worry about, even if attacks such as these are unlikely to derail a campaign that – given most members vote early – might well have already won. What sets Long-Bailey apart is not ideological continuity but institutional continuity: in Unite, Momentum, the smaller, more radical trades unions, and the ecosystem of new left media outlets, she is sustained by the same interests and power-brokers that sustained Corbyn’s internal hegemony for so long. While they won’t prevent Starmer bringing that era to a close, their shift to attack mode does offer a glimpse of the internal resistance that awaits him should his leadership deliver what so many on the left expect: compromise and disappointment.

• Patrick Maguire is a political correspondent at the New Statesman