The backbone of most political parties is made up of MPs who, having enjoyed successful careers outside of politics, enter parliament in their forties or fifties. In the Conservative Party, they are former heads of mergers and acquisitions, partners in top-end law firms, and entrepreneurs. In Labour and the Liberal Democrats, they are the former chief executives of charities or have reached senior positions in the public services. They tend to serve effectively as junior ministers and on select committees, usually but not exclusively tapping into their previous area of expertise.

What they don’t tend to do is run ruthlessly well-organised campaigns for the top job. Which is one reason why Keir Starmer’s confident, polished start to his tilt at the Labour leadership has surprised his opponents. The barrister began his bid with an interview in the Guardian that was perfectly calibrated to appeal to the party’s rank-and-file activist base, before unveiling a slick video that had all the necessary elements to travel far and wide on Facebook. (Facebook and the Guardian’s website are, along with the BBC, the main outlets where the Labour leadership race will be fought and won.) The video tapped into Starmer’s successful previous career – including his efforts to secure justice for Stephen Lawrence and his pro bono work defending environmental activists against McDonald’s – and set about pre-emptively defusing, as best as he could, the attack lines against him.

The shadow Brexit secretary received a further boost when YouGov, which has correctly predicted the outcome of every major party election across all the parties since it was founded in 2000, released a poll showing him 22 points ahead of the chasing pack. One sign that his campaign is rattling his opponents is that they have started to grumble about it. Supporters of Lisa Nandy and Jess Phillips have confined themselves to doing so privately, but it cannot be long before they echo Rebecca Long-Bailey, who began her bid with a thinly veiled public complaint. She said that she “didn’t emerge from the election with a ready-made leadership campaign because my every effort during the election went into campaigning for a Labour victory”.

Every fair-minded observer of Labour politics knows this is untrue: Long-Bailey released her own sharp video, complete with personal logo, a month before the election and has long been mentored and promoted as Jeremy Corbyn’s true heir. But it’s a smart attempt at turning a weakness – a flat-footed start to campaigning compared to that of her main rival – into a strength, and is one reason why her hopes of winning the leadership are still strong.

It is true that in terms of policy there is scarcely any difference between Starmer’s pitch for the leadership and that of Long-Bailey. In parliament, some supporters of Jess Phillips, the right-most candidate for the position, think that Starmer’s approach means that he has no hope of winning the next general election. Neither the left or right wing of the party can quite decide whether to treat Starmer’s positioning as a genuine statement of his values. MPs supporting Long-Bailey tend to think that Starmer’s left-leaning position is a feint that will be abandoned once he gulls Labour’s rank and file into supporting him for the leadership. (Although Long-Bailey herself has implicitly accepted that Starmer is a true believer.) But it is the allies of Phillips, who is marketing herself as a no-holds-barred truthteller, who feel the most comfortable suggesting that Starmer is presenting himself as something he is not.

The difficulty for Starmer is that it’s not just his opponents who aren’t sure what to make of him. His allies aren’t certain who the real Starmer is either. Is he the pragmatist who Labour’s earliest advocates of a second referendum derided as cautious and concerned primarily with keeping the Parliamentary Labour Party united? Is he a committed Remainer who has all along planned to move Labour to a second referendum position? The Labour MP Andy Slaughter once observed that if you talked to the arch-Brexiteer Kate Hoey and the ultra-Remainer Chuka Umunna, the one thing that they both agreed on was that Starmer was doing a brilliant job as shadow Brexit secretary. Did that united support collapse because of forces outside Starmer’s control, or was he exposed as a limited politician?

Is he a lawyer who stood up for the powerless? Or is he the tough-as-nails director of public prosecutions who stood firmly behind the police?

The reality is that Starmer, who became an MP in 2015, did not work for free against the might of McDonald’s in the mid-1990s in order to boost his chances of taking control of a shattered Labour Party a quarter of a century later. His record at the Bar and in the Crown Prosecution Service means that we have a far greater sense of where Starmer will be on justice – tough on corporations, but tough on crime too – than on other issues. Even on Brexit, where he impressed many Labour MPs, the depth of his pro-European commitment is still unclear: he became the face of Labour’s second referendum policy, but showed no hesitation in declaring that the election result spells the end of the Remain cause.

In that respect, he is the very model of an MP who has traded in a successful career for a stint in politics. The difference is that for him to be more than simply an effective candidate for the Labour leadership, he’ll have to do what most MPs who come to politics in middle age do not: acquire a definition outside their area of previous expertise. The great hope of his opponents, within the Labour Party and outside it, is that Starmer cannot acquire greater definition without losing support.