“That’s a pretty amazing interview, I have to say,” John Barrett, a former associate counsel in the Iran-Contra investigation and a law professor at St. Johns University, said of Nunberg’s appearance on MSNBC. “‘It’s hard to cooperate with law enforcement’ is just not a valid reason to refuse to cooperate with law enforcement.” Barrett points out that the the government could argue that, if gathering the relevant emails is too burdensome, prosecutors could take possession of the server and perform the search themselves.

Pressed by Tur about whether he believed Mueller “had something” on Trump, Nunberg said: “I think that he may have done something during the election. But I don’t know that for sure.”

That admission on its own may sabotage whatever chance Nunberg had of fighting the subpoena. “It’s the kind of statement that obviously must pique the interest of Mueller and his office, and it cries out for further questioning,” said Barrett.

Later, speaking to CNN’s Gloria Borger, Nunberg elaborated on the same sentiment—even confirming that the special counsel was now looking into Trump’s business deals. “The way they asked about his business dealings, the way they asked if you had heard anything even while I was fired, it just made me suspect that they suspect something about him,” Nunberg said. “He may very well not have done anything, but the other thing I will tell you, is regardless of whether or not he had money coming to him during the election, okay, during the general, he won that election. And he has to get credit for it.”

Later, Nunberg added, “Trump may have very well done something during the election with the Russians. If he did that, I don’t know. If he did that, it’s inexcusable if he did that.”

“By admitting that Trump ‘may have done something’ and that he may have specific knowledge about that something, Nunberg may have provided a probable cause tipping point that would allow Mueller to obtain a search warrant for all the information—i.e., email content—that Nunberg is presently refusing to provide,” Dave Gomez, a former FBI agent and a fellow at George Washington University’s Center for Cyber and Homeland Security, told me in an email.

A grand-jury subpoena to turn over information can be fought—either by alleging an excessive burden, or invoking the Fifth Amendment, or seeking to narrow its scope. But a warrant based on probable cause would allow Mueller to seize the emails himself.

“A search warrant is for an involuntary seizure of property. It requires an affidavit presenting probable cause for the search and/or seizure, sworn to by the investigator, and approved by a judge,” Gomez said. “The phone company or email provider maintains copies of content, but requires a search warrant for access. Which is why Nunberg’s public comments are interesting. He clearly did not clear that statement with his attorneys.”