And we’re off! Labour’s leadership and deputy leadership races are officially underway: the party’s ruling National Executive Committee has set out the timetable, and the candidates have all declared, with Rebecca Long-Bailey officially launching her campaign with an article for Tribune.

The timetable means that it will be a three-stage contest. Over the next week candidates will jostle for nominations among the parliamentary party in the Westminster and European parliaments (the latter group retain their right of nomination until 31 January), while the next month will be spent seeking the additional nominations they need: either from trades unions and other affiliates, or from ordinary Constituency Labour Parties. A good way to understand it is this: you need either two trades unions and another affiliate, like the environmentalist group SERA, to make the ballot via the affiliate route; or the support of 32 Constituency Labour Parties to make the contest via the membership route.

Because MPs will winnow the field first, this process makes it easier for more candidates to make the ballot. Long-Bailey is guaranteed to get on via the trades union route and Keir Starmer is likely, but not certain, to be able to get on via that route as well. But for the chasing pack – Jess Phillips, Emily Thornberry, Clive Lewis and Lisa Nandy – they are likely to need constituency nominations to make the contest proper. That not all four of those candidates will make it past the MPs' stage will make it easier for the survivors to get the CLP nominations they need – though it is not certain that they will be able to do so.

One of those candidates could surprise the odds and win, but forget the polls: this is still Long-Bailey’s contest to lose. She will be able to unveil the endorsements of every big name Corbynite you care to mention – including that of Jeremy Corbyn himself, who I think is likely to break the unwritten convention that the sitting leader does not endorse.

Yes, Starmer is, thus far, fighting far and away the best campaign, but that might not be enough. Look closely at Long-Bailey's opening pitch, though, and you can see why Team Starmer has reason to hope.

There's an intriguing dissonance between Long-Bailey’s argument that she is the candidate to defend the current slate of policies, but that she will open up the party's agenda to consultation with the public, the trades unions and the membership. What’s the consultation for, then?

Add that to her rollout on the Today programme this morning, in which she wouldn’t commit to continuing the free movement of people after Brexit, but would commit to using the nuclear deterrent – an explicit move away from Corbyn's position – and you see the implicit divergence from Corbyn that she wants to pursue: the phrase “progressive patriotism” might have vanished since her original launch in the Guardian but the thinking is still there.

The implicit argument in Long-Bailey's pitch is that the economics worked brilliantly but, by pivoting on issues about nation and security, the party can win on a Corbynite ticket. It's a tricky needle to thread as far as the party membership's own priorities on migration in particular are concerned. It's trickier still if you need to – as Long-Bailey does – set out positions where Starmer and Lisa Nandy (if she makes the ballot) cannot easily echo you.

Long-Bailey has big institutional advantages – but at present, her campaign is very heavily depending on them if she wants to win.