It is astonishing that the Labour leader is so lacking in political worldliness that he did not demand bullet-proof evidence be presented to him before making his allegations. Now he is left floundering as the Prime Minister challenges him to "put up or shut up".
Yesterday's revelation by NewstalkZB's Barry Soper that the prime source of the leak was a former GCSB official who is in a relationship with the Labour leader's spin-doctor Fran Mold also compounds Shearer's predicament.
He won't confirm or deny the Soper revelation saying he doesn't "declare his sources".
But with no sense of irony, Mold later released a press statement under Shearer's name saying the "PM must confirm or deny Dotcom comment". (Realpolitik dictates that John Key doesn't have to do anything until Shearer produces the video, Fran.)
It Key wants to get heavy he could demand that the GCSB fully investigates the links between Mold, her partner, his former close colleagues at the external intelligence agency and Shearer to see if they have breached the law. It's doubtful Key would want to prolong the Dotcom embarrassment given the other issues on his plate. But the State Services Commission did appoint an investigator to try to track down the Ministry of Foreign Affairs and Trade (Mfat) leaks.
Senior Labour figures must be rolling their eyes at the way their leader's crusade has blown up in his face.
There's really not much else that one can say. The silence of Labour's usual soc-med afficiandos is deafening; none has publicly supported their leader. David Shearer looks completely isolated.
And any traction that Labour had been getting with its allegations against John Key has well and truly gone. David Shearer is the story now. Not only that; he seems to have made his chief press secretary's position untenable.
David Shearer was cock-a-hoop when 3News and Campbell Live went to air on Thursday. 36 hours later, he's looking more like coq-au-vin.