Clive Lewis’s off-again, on-again relationship with the Labour grassroots is on-again. The shadow business secretary has vowed to vote against triggering Article 50 and resign from the shadow cabinet if needed, unless he is persuaded that the final bill avoids a hard Brexit. (He will still vote for triggering Article 50 at the second reading.)

For much of the lifetime of the Corbyn project, Lewis has been the preferred successor of many in the grassroots. He also enjoys the support of most of the small band of Corbynites in the commentariat. But in signalling he would vote to trigger Article 50, he opened up a potentially fatal breach between him and party members.

For the last 20 years, the Labour membership has been overwhelmingly pro-European, but only in the same sense that Britain is overwhelmingly a Christian country. Most might like the idea, some might even attend church at Christmas, but very few were genuinely devout. That was why Corbyn – a lifelong Eurosceptic who voted against every single European treaty that came before the Commons in his time as an MP – was able to win a landslide victory in 2015 among a pro-European party, despite telling the New Statesman that he had not “closed his mind” to the possibility of voting to leave the European Union.

But the Labour grassroots is undergoing something of a religious revival as far as pro-Europeanism is concerned. I’m reliably informed that more than 7,000 people have quit the Labour Party in the last week over the party’s Article 50 stance. For many inside and outside Labour, supporting a Remain vote has become a proxy not just for how you feel about the EU but a wide swathe of issues: pro- or anti- immigration, for or against social liberalism, and so on.

A lot could happen between now and the next Labour leadership election, but, as things stand, voting against Article 50 looks to me to be a prerequisite for victory. For Lewis, there is the added risk that his marginal seat of Norwich South – which voted to Remain by a heavy margin – would almost certainly be lost if he voted to trigger Article 50. While many of the big beasts in the shadow cabinet – Diane Abbott, Emily Thornberry, Keir Starmer, and Jeremy Corbyn himself – have large pro-Remain votes in their constituency, they have much bigger majorities and are therefore at less risk from a revolt of Remainers.

Whereas it would be brave, to put it mildly, for Lewis to vote to trigger Article 50. So the politics of voting against triggering it are fairly open and shut from Lewis’ perspective.

But I wouldn’t make him the frontrunner just yet. As Lyndon Johnson was fond of saying, the most important thing in politics is to be able to count. The numbers that matter as far as Lewis is concerned are 15 per cent – the number of people in the parliamentary Labour party who have to sign a candidate’s nomination papers – or, if the attempt to reduce the threshold succeeds, five per cent. Or, in whole numbers: 35 or 12 MPs respectively. Although there are some Corbynsceptic MPs who are open to the possibility of a Lewis leadership, it is hard to plot a path to the ballot for him unless he is the designated successor of the party’s Corbynite wing.

As I wrote in November, Rebecca Long-Bailey, currently the shadow chief secretary to the Treasury, is now widely expected to be the preferred successor come the next leadership election, for four reasons. Over at PoliticsHome, Kevin Schofield tips her to receive a big job in the post Article 50 reshuffle. The first is that she has a majority of 12,541, capable of surviving even a landslide. The second is that she has a record of proven loyalty, both to the leadership and to the trade union left. Her personal proximity to the trade union left is the third reason. The fourth reason is that there is an expectation that there will be an overwhelming pressure within the parliamentary Labour party that the next leader be a woman. It wouldn’t be wholly surprising if that results in an all-woman shortlist.

If the support of the party’s Corbynites flows to Long-Bailey, it will be hard to plot a path to the ballot for Lewis as well. His situation at the moment looks to me very similar to Chuka Umunna’s; he had committed enough heresies to leave him without a base on the party’s soft left, but had not yet convinced the party’s Blairites that he was one of theirs. In the membership, if Lewis does vote against triggering Article 50, he could be almost anyone’s candidate. The difficulty is that can easily translate into to being nobody’s candidate.