If Jeremy Corbyn doesn’t take care his shift in immigration policy will take him to an even worse place than he was in already.
Those Labour liberals who think, as he used to, that free movement of people for work within the EU is a thoroughly good thing are already accusing him of cowardice, with his statement that he is not “wedded to free movement as a point of principle”.
But his conspicuous concerns about free movement do not appear to be about the job and wage prospects of white working class voters – or those who are now turning away from a Labour Party they think is deaf to their anxieties and have been moving towards UKIP.
What really fires up Corbyn, as is clear both from the published extracts of a speech to be made later today and his interview for the Today Prog, is what he sees as the terrible exploitation of East European workers, shipped over here to work for undercutting wage rates on zero hours contracts.
The sense he conveys is that his priority is to protect them, which is laudable and decent – except that East European “agency” workers are adults and have made a choice to come here, and even if they’re grateful to him they cannot take him and his party to power.
What is more, he absolutely refuses to discuss possible numerical targets for immigration.
And there is another substantive difference between him and the Prime Minister - in that she says control of immigration trumps access to Europe’s single market, and he cannot bring himself to say that.
So just maybe, and under pressure from his trade union supporters, Corbyn has moved just far enough to ease some of the tensions within Labour on this contentious question.
But he hasn’t delivered an easy-to-understand policy that is likely to do much for Labour’s woeful standing in opinion polls.
To be clear for many people there is an attractive “authenticity” in Corbyn’s conspicuous reluctance to trim his long-held views in the cause of becoming electable.
But when he also says, as he did this morning, that he would be happy to join the Southern Railway picket lines, and that he is in favour of a law that would make it illegal to pay more than an unspecified maximum, some will see him as a grizzled student activist rather than a prime minister in-waiting.