In the months after Edward Snowden's revelations it was reported that a "no spying" deal between Germany and the US collapsed because America refused to call a complete halt to its eavesdropping ways.
The allegation that this latest row is about the US spying on Germany's own investigation into Snowden's initial claims bolsters that theory.
It could explain why Germany is so outraged and it blasts the Obama administration's assurances that it would amend its espionage tactics.
Germany's opposition to the Iraq war in 2003 was a low point in US relations, but this latest controversy is eclipsing it.
Chancellor Angela Merkel's efforts over the last decade to build a stronger relationship are now being severely tested.
For months Germany has been seeking clarity from the US on its surveillance of the country and its leaders.
Clearly that hasn't come.
Instead there may have been even more spying, which is why Germany has made its most outward expression of anger yet.
Chancellor Merkel - left to wrestle with the knowledge that her own phone was listened to by the US - says the two countries have better things to do than "waste energy spying".
Her Finance Minister, Wolfgang Schauble, was a little more scathing, saying: "With so much stupidity, you can only weep."
As is the norm, the US won't comment on intelligence issues, but behind the scenes diplomatic channels will undoubtedly be buzzing.
Germany has to express criticism without jeopardising its valuable relationship - while the US has to convey regret without surrendering its intelligence tactics.
Falling out isn't in either's interests, but with each revelation, staying friends becomes all the more challenging.