This is a defining moment for the Corbyn project, and attacks over antisemitism and Palestine must be firmly opposed or they will escalate to chilling effect, argues Chris Nineham

Given the intensity of the campaign and the appalling nature of the slurs against Jeremy Corbyn, it should be obvious that the widest, firmest possible defence of his leadership and his politics is necessary.

There are two misconceptions that can hold people back. First is the idea that the whole antisemitism controversy only really has traction inside the Westminster bubble and that it is having no effect on wider public opinion. This seems unlikely. However surreal they may seem to people who know Corbyn’s record, the relentless attacks are at a minimum going to be raising questions in some peoples' minds, the more so because they are going largely unanswered. But the crucial thing is that the attackers are not mainly concerned about the wider public. They are in fact focussed on Westminster and official politics, the arena in which Corbyn has fewest supporters and is at his weakest.

The whole point is to embolden his enemies there and intimidate his friends, to force Corbyn to beat a retreat on one of his defining political positions and preferably make life in Westminster impossible for the leadership.

This leads to the second misconception. Many seem to think that our plan should be to close down the whole debate so that politics can move on. The idea is that by conceding on the IHRA code, with caveats introduced in the Labour Party code of conduct, the whole discussion about antisemitism will be wrapped up and normal politics will resume. Where is the evidence for this?

Corbyn himself has apologised or numerous times – unnecessarily in my view – for remarks or actions that could apparently have been construed as antisemitic. The idea was to draw a line under the discussion. Each time such tactical retreats have only encouraged his enemies. Each time, sometimes with a pause for breath, sometimes not, the attacks have simply been taken to a new level.

The mistake is to believe things can’t get more serious still. If the NEC does accept the IHRA definition with all the examples, even with the caveats of a rewritten code of conduct, this will almost certainly greenlight a new phase of attacks. Changes to the code of conduct will most likely be treated as a footnote to the main story: a major retreat from a political position central to Corbyn's whole project.

From that point on, statements and actions of solidarity with Palestinians that have become part of the DNA of the movement and the left here will be open to challenge. The unions and all sorts of other bodies will immediately be looking to their own rulebooks and their members' conduct. A chill wind will blow through the whole movement and of course Jeremy Corbyn’s behaviour past and present will be under even heavier scrutiny.

Any other prediction is to misjudge the nature of the assault that’s taking place. It is absolutely necessary to be concerned and vigilant about antisemitism. But as many people have documented the current hysteria is completely disproportionate to the problem that exists in the Labour Party. Comments like that made by Johnathan Sacks comparing Corbyn to Enoch Powell are so palpably absurd that they can only be understood as part of a wider agenda. The aim is to both to roll back support for the Palestinian cause and to damage the Corbyn leadership, and, if that is the case, success will only embolden the attackers.

Underlying all this no doubt is a sense that the attacks are so relentless they simply can't be resisted, and that the die is anyway already cast. This is to miss one essential factor in the situation.

There are hundreds of thousands of Labour Party members, Corbyn supporters, activists and voters who sense that these attacks are disingenuous and dishonest and who are deeply worried about what will happen to Corbyn and the Palestinian cause in the case of a retreat. These are the people that have rallied to Corbyn's defence when he has been under attack a number of times already. Successfully. These are the people who got Corbyn elected in the first place. These are the people who got the vote out in the general election last year.

Every single voice that is raised against the witch hunt now, every clear statement about what is at stake, every vote for the NEC code next Tuesday will give that bit more confidence to the people who make up the movement anyway. It's only this movement mobilised that can keep the Corbyn show on the road. It's time to stand up and be counted.