Briefly, Nunberg had been an on-and-off political adviser to Donald Trump, and his role with the Trump campaign came to a complete end in August 2015. His relationship with Trump and the Trump campaign ended badly, but everybody moved on.
As I understand it from people who were there at the time, Nunberg never had a defined role, was never in a management capacity and was basically just a gadfly. The only thing that makes Nunberg interesting or significant today is that he is now the focus of some part of the Mueller investigation.
It is difficult to imagine at this late date what possible information Nunberg could have that is relevant to any aspect of the Mueller probe. And that in and of itself tends to confirm some of the worst suspicions many have about the investigation.
Particularly, the people Mueller has hired - several of whom have also contributed to Hillary Clinton and other Democratic candidates, or represented Democrats - essentially have a free hand to go after Republicans no matter how peripheral they might have been to the 2016 campaign or to Mueller's original charter.
No one I have talked to who was associated with the campaign and knew Nunberg can even fathom what he might have to offer.
So, when you consider the breadth of what Mueller's subpoena has asked Nunberg for, it is easy to think the investigation is overreaching and perhaps making a wild play in hopes of finding something, anything to tarnish or somehow implicate the president.
After all, Mueller's subpoena appears to be asking for several years of "records of any kind" pertaining to President Donald Trump and nine other individuals - many of whom are either no longer working in the White House or never joined the administration to begin with.
By any measure, the subpoena seems to be overly broad.
The bottom line is that Mueller's pursuit of Nunberg suggests that there is no limit to what he or the partisans working for him will do next.
There are hundreds of Trump campaign staffers, volunteers and contributors who were in closer proximity to the real campaign than Nunberg ever was.
The pursuit of Nunberg is troubling. He seems personally tormented, and no one who knows anything about his brief role in the early summer of the 2015 Trump campaign can justify the sudden interest the special counsel has taken in this marginal character.
I've been pretty sympathetic to the Mueller probe, and I remain respectful of Mueller himself, but this is puzzling.
Mueller's latest move either means he is wrapping up his investigation but taking an unnecessarily harsh look at a few remaining players, or he is desperate, has nothing on Trump and is grasping at straws.
Mueller must be aware of how the appearance of his pursuit of Nunberg diminishes the overall credibility of his investigation.