Judge Sullivan does not seem like a happy camper.

I can't imagine Sullivan will ultimately decide to proceed with Flynn's conviction and sentencing, but he's sure as heck going to put AG Barr's new legal theory to the test before he lets this go.

Keep in mind the system is intended to be adversarial, but this isn't unprecedented. The courts at all levels have often appointed amicus to represent the interests of the U.S. when the U.S. declines to defend itself.

The retired judge appointed as amicus to argue against DOJ's motion to dismiss the charges against Flynn co-wrote this op-ed about the Flynn prosecution on Monday:

"The Flynn case isn’t over until the judge says it’s over." https://www.washingtonpost.com/opinions/2020/05/11/flynn-case-isnt-over-until-judge-says-its-over/

To return to this, don't forget, Judge Sullivan has been put in this position before. In 2009, he ultimately agreed to AG Holder's request to dismiss the case against Sen. Ted Stevens—after Stevens had been found guilty by a jury.

But he put the DOJ through the ringer first.

Sullivan was famously unhappy about being put in that position and, in response, opened an inquiry into DOJ's decisionmaking in the case.

So it's not unprecedented that he'd look behind AG Barr's new-found skepticism of 1001 prosecutions.