Accusations that the NSA has listened in on Chancellor Merkel's conversations are not conducive to positive German-US relations. Interestingly, the fact that the White House is saying that they 'are not' monitoring and 'will not' monitor Merkel, suggests that 'they have' monitored her in the past. To be sure, as I noted yesterday, there are worthwhile reasons behind US intelligence collection operations in Europe. Still, targeting the phone of a close ally (especially a head of state and especially one as friendly as Merkel) is a dangerous gamble. It risks significant blowback in terms of personally alienating a valued American friend. The NSA will have known this. Correspondingly, I assume that Merkel was targeted for a short time and in pursuit of specific information. Perhaps in regards to her position during a conference/financial negotiations (international meetings are a playground for intelligence officers).
There's another point here; as Marc Ambinder (a top journalist on the NSA) notes, if Merkel was indeed targeted, then why wasn't her position as an intelligence source more highly classified? Ambinder hints at the larger truth. If she was monitored, Merkel was effectively a deep cover source. In that regard, it's truly ridiculous that Snowden was able to gain access to such an operation. He was a contractor, not the Director of the NSA. As I've argued before, the US Government has a serious problem with its protection of its highly classified sources.
Of course, all of this raises the broader question as to what other information Snowden might have given Greenwald. Does he have agents/officers details? The British certainly think so. Based on what's happening at the moment, we must assume that Greenwald is upping the ante. This may signal how he'll conduct himself at Omidyar's new media endeavor. Ultimately, this is what will most concern the US Government - signal intelligence programs can be reconstructed. Humans cannot.