Labour MPs have a red line in the same way that the world has a horizon: it’s clearly visible, there are plenty of people around to tell you where it is, but it is, somehow, always safely in the middle distance. There was once a time in which Corbynsceptics saw the treatment of Luciana Berger, Britain’s most prominent Jewish MP, as a line in the sand. If she had no future in the Labour movement, neither did they. Berger then left the Labour Party – and only seven of her colleagues opted to follow her out of it. (Berger has since joined the Liberal Democrats.)

There was a time, too, when the fate of Margaret Hodge, the Labour MP for Barking – like Berger, a prominent and vocal critic of Jeremy Corbyn and all his works – represented the point of no return for Labour MPs. Now Hodge, who is Jewish, has become the second Labour MP to face a reselection contest. Once again, a Corbynsceptic red line turns out to be drawn in pencil rather than ink. MPs confine themselves to concerned tweets about the threat against Hodge, but do little beyond that.

Even those MPs who had resolved to leave the last time that Hodge’s position was under threat now say they have no intention of heading for the exit.

Why? What is going on?

Labour’s Corbynsceptics still represent a minority on the party’s ruling National Executive Committee, among the party membership and at every level of the party’s salaried staff. But they are in the grip of an unusual experience: victory. They are winning, and winning reliably, in what might yet prove to be the party’s most important contest: the battle to reselect sitting Labour MPs.

Neil Coyle, the Labour MP for Bermondsey and Old Southwark, Corbyn’s most vocal and vituperative critic, has been reselected as the Labour candidate. Alison McGovern, the chair of Progress – the organised home of New Labour – has been reselected in Wirral South. Lucy Powell, who quit Corbyn’s shadow cabinet and conducted cross-party talks in an attempt to secure a Brexit deal, is back in as the party’s candidate for Manchester Central.

The successes of these MPs are even more surprising given the odds against them. Jeremy Corbyn’s Labour, like the old party it replaced, uses the rule book as a weapon with which to beat its rivals.

Before Corbyn’s leadership, incumbent MPs were protected by a system that was engineered to ensure that a sitting Labour MP could protect themselves from any challenge provided they were well-organised.

Under Corbyn, a small tweak to the rules has made it easier for party members to trigger a full selection process: a change designed to facilitate the removal of dozens of Corbyn’s most trenchant critics. But the promised revolution has failed to arrive. Just two MPs – Hodge and Diana Johnson – have so far failed to pass the new trigger ballot, and all the indications are that most of the Parliamentary Labour Party (PLP) will be reselected.

The circumstances of both cases are unusual and suggest that most Labour members still prefer to avoid a full contest. In Hull North, Diana Johnson, who is not from Hull originally, was selected in 2005 via an all-women shortlist, a process that several people in the local party still oppose. While she has been quietly loyal to the leadership on many issues, she has been a vocal critic of the party’s handling of anti-Semitism in its ranks. In addition, she has an organised opponent – Aneesa Akbar, a local councillor – who already has a website and has bagged the endorsement of Hull City Council’s leader, Steve Brady.

Margaret Hodge has been one of the most vocal critics of the Labour leadership on many issues, and several ambitious local councillors have their eyes on the seat.

Neither Johnson nor Hodge were able to command a majority of local party branches and thus fight off a full selection process. In both cases, they were also victims of what allies describe as bad luck and critics describe as poor organisation.

This raises a difficult question for Team Corbyn. Transforming the PLP is an essential prerequisite to maintaining their control of the party and staffing the ranks of a future Labour government. And yet, they cannot manage to trigger selection contests in all but a handful of cases.

That means that for the first time since Corbyn’s second landslide leadership victory in 2016, his internal critics are daring to hope that they might retake control of the party from the left – a prospect that seems ever closer because of Labour’s disastrous position in public opinion polls. Many Labour MPs have anxieties about campaigning to make Corbyn prime minister in a general election. However, because Corbyn looks so far off from achieving that aim, even with the Conservatives in crisis, those worries feel less acute.

This line of thinking has two obvious risks. The first is that Corbyn may defy expectations in an election campaign, as he did in 2017. In that contest, the so-called brilliant defeat, he increased Labour’s share of the vote by 10 points, to 40 per cent, and deprived the Tories of a majority, securing his position as leader.

The second risk is that the price of a fourth successive election defeat for Labour, stretching back to 2010, is yet another Conservative government. The consequence of such a defeat would be another Labour civil war. So whatever the outcome of the next election, Corbynsceptics are risking a great deal on the belief that they can finally do something they have never managed: get the better of Jeremy Corbyn and take back control of the party.

Stephen Bush is political editor of the New Statesman