In politics, opportunities for supreme power are rare and fleeting. Yet rather than making challengers to Sir Keir Starmer more ruthless, this truth seems to have made them more cautious. The health secretary, Wes Streeting, resigned from the cabinet but did not launch a leadership bid. Rather than provoke a contest, Mr Streeting’s message to Sir Keir was that since his authority was gone, his duty was to depart and enable an orderly transition rather than cling to office.

If the Labour leadership were truly up for grabs, winning it would require opportunism, a feel for elite collapse and a willingness to defy both the party establishment and orthodoxy. Those who successfully seize the crown – Lloyd George, Harold Macmillan, Margaret Thatcher and Boris Johnson – recognise their moment and act decisively. These leaders were also not subject to the Labour party rulebook.

Sir Keir’s grip is loosening, but replacing a sitting Labour prime minister is institutionally and politically difficult. Not least because any successor would still need to unite large sections of the parliamentary party and trade union movement, as well as the activist base and wider membership. In the meantime, Britain faces a damaged prime minister, a fractured ruling party and no clear route out of a political crisis – just as another brutal cost-of-living squeeze takes hold.

If Sir Keir stays in post and Mr Streeting or anyone else wants to challenge him, then under Labour’s rules they need a fifth of Labour’s MPs to back them. Sir Keir automatically gets on to the ballot as the incumbent leader. Getting 81 MPs to publicly back a coup is extremely difficult unless the leader’s sway has already evaporated. Sir Keir could follow Mr Streeting’s advice and resign for a caretaker leader. That may now be the least damaging option. But Labour’s rules make swift succession difficult, requiring candidates to canvass support from constituency parties and trade unions.

Polling by Persuasion UK suggests Labour’s crisis is existential, not a problem of presentation or leadership style. A sharper version of Sir Keir’s politics won’t resolve the problem. While MPs panicked over Reform UK, the polling showed Labour’s voters mostly stayed home or turned left to the Greens and Lib Dems. Many defectors felt abandoned by Labour’s visionless triangulation. Simply replacing the health secretary and ploughing on regardless, as implied in Sir Keir’s letter to Mr Streeting, would be a mistake.

If it is to renew itself, Labour needs a leadership contest. Ideological fights can deepen division. But Sir Keir took office before Labour had resolved questions over fiscal restraint, social fragmentation, whether green transition can raise living standards and whether competence alone can hold together an electoral coalition. That is why figures like the Greater Manchester mayor, Andy Burnham, and the former deputy prime minister Angela Rayner matter beyond personal ambition: each represents a different emotional tone and understanding of state, nation, economy and society. Blocking Mr Burnham’s Westminster return would make Labour look scared of renewal.

In 1968, when Sir Keir’s favourite Labour prime minister, Harold Wilson, looked weak after devaluing the pound, many MPs wanted his chancellor, Roy Jenkins, to take over. Jenkins dithered and the moment passed. Wilson remained prime minister. Labour’s history suggests that politicians frozen by norms or fear rarely wear the crown. Unlike Jenkins, Mr Streeting forced Labour’s succession crisis into the open. Mr Burnham is now testing whether it can become something larger than elite discontent.