Labour leader David Shearer has forgotten - if he ever knew - Rule Number One of political scandal-mongering.
Make sure you have damning evidence in your hand before launching a crusade designed to out your political opponent as an outright liar and shorten their political career.
It's simply not credible for Shearer to be insinuating the Government Communications Security Bureau must have wiped hard drives that supposedly contained multiple copies of a video proving Prime Minister John Key has lied about the Dotcom affair.
This was always going to be a high-stakes allegation.
If the videos did exist, the Labour leader's team should have made sure they had a copy locked away ready to be unveiled the moment Shearer had trapped John Key into making a denial. This is school for scandal 101.
Alleging the GCSB has effectively "trimmed for trial" (as they say in the legal game) by getting rid of the videos once the heat came to protect their prime ministerial boss doesn't cut it.
As anyone who has mounted big public investigations knows (be they journalists or politicians) evidential material is much harder to get once the blowtorch goes on the organisation or person suspected of leaking the goods. That's because any leaker, particularly from out of officialdom, will be wanting to cover their tracks in case they get fired or criminally charged for leaking confidential material.
In the GCSB's case, it is also a relatively safe bet that the Security Intelligence Service (SIS) will be all over the organisation to ensure other so-called "leaks", including about matters of national security, are not in the offing.
It's not uncommon for protagonists to hire private investigators to track journalists, bust into media offices and try to get leaked documents back. If the stakes are high enough that is exactly what happens, as it did in a newspaper office where I worked during the 1990s "Winebox" tax-dodge affair.
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.
More experienced hands like Phil Goff - who so comprehensively fitted up Foreign Minister Murray McCully by quoting directly from Cabinet papers to expose a restructuring fiasco at Mfat - will be looking askance. So too that master of the political dark arts Trevor Mallard.
The reality is Shearer didn't need to ratchet up the Kim Dotcom affair any further.
Key was already battling a credibility issue because of his failure to recall that Dotcom's name was mentioned during a GCSB briefing on February 29 - well ahead of the September 17 date he originally claimed as the first time he had heard of the bureau's involvement in unlawfully intercepting Dotcom's communications. The GCSB has been left off the hook when it should still be facing public scrutiny over its unlawful spying on Dotcom.
David Shearer has scored a glorious own goal - the caucus knives will be sharpening.