Mounting a challenge will simply look self-serving if, having backed Shearer yesterday, Cunliffe's supporters then turn around and try to oust the current leader.
For his part, Shearer is playing divide-and-rule. He has disciplined Cunliffe, dumping the New Lynn MP from Labour's front bench and stripping him of his prized economic development and associate finance roles.
Shearer has not given Cunliffe's backers in the caucus the same treatment. He is planning a major reshuffle of Labour's shadow Cabinet. He is clearly leaving those MPs to work out where their best interests lie.
As for Cunliffe, he is now on notice to toe the line. If he continues to exhibit the disloyalty he so openly displayed at Labour's annual conference last weekend, he will be suspended or expelled from the caucus.
He has since found himself on the receiving end of roastings from senior colleagues both in public and in private. Those MPs are simply flagging that they could not work under him. That is the main reason why Cunliffe will not be able to trigger a leadership election in February.
Labour cannot afford to end up with what would be a hopelessly divided caucus. That is not a recipe for good government - or even good Opposition. It would poison Labour's chances of winning the 2014 election.
That is the bottom line. And those few MPs still inclined to back Cunliffe know it.