Andy Burnham has committed to bringing the welfare bill down, but he knows just how the high the political stakes are.
He saw how last year's welfare rebellion marked the beginning of the end for his predecessor in Downing Street.
Sir Keir Starmer's authority was shredded when 120 - more than a quarter - of his own MPs threatened to derail his reforms.
To defuse this, Sir Keir was compelled to guarantee that existing claimants of personal independence payment (Pip), the main disability benefit in England and Wales, wouldn't lose out.
Even then, 49 of the 120 potential Labour rebels still voted against their own government.
Next week, a review from former New Labour cabinet minister Alan Milburn has the capacity to create another internal row in Labour's ranks.
Milburn has spent a year grappling with how to reduce the nearly one million young people who are not in employment, education or training (Neets).
In an interview with the Times, he has now confirmed he is set to recommend cutting benefits for some 16-24 year olds who currently receive Pip, or the enhanced health-related payment of Universal Credit.
Taking benefit cuts to the Parliamentary Labour Party would usually have a similar effect to adding phosphorous to water.
