As the only Labour politician with any appeal beyond the party's own fragmenting supporters (unless you count Ed Ball's Strictly fans), London mayor Sadiq Khan used his political clout to ram home a clear message to Jeremy Corbyn: all his moral resolution, all his principled stances and all his hardcore supporters can achieve nothing meaningful unless he wins power.
In fact, 'power' was a word Khan used no less than 38 times in the speech he delivered at the Labour party conference.
Not exactly subtle, then. But right now, Khan is the only Labour figure with enough of his own support to tell Corbyn exactly what he thinks – i.e. that he is incapable of winning an election – without being dismissed as an out of touch Blairite defending old politics.
Khan - who backed Owen Smith's failed bid to wrestle the party leadership away from Corbyn - may just be the only man who can get through to the #JezWeCan crowd and persuade them to back someone with approval ratings that may actually one day translate into votes.
Someone, perhaps, like Sadiq Khan.