What exactly is the "Trout" in this D.C. Circuit Court of Appeals opinion? Does it suggest a political motive of a judge?

Question

Edited to reflect why I feel this question is on-topic here.

The following is excerpted from Politico's Appeals court deals setback to Flynn’s attempt to end DOJ case against him:

The D.C. Circuit Court of Appeals, sitting en banc, voted 8-2 to reject Flynn's effort to dismiss the case immediately. The court’s ruling Monday also rejected efforts by Flynn to remove District Court Judge Emmet Sullivan from the case over allegations of bias.

The unsigned majority opinion rejected arguments from Flynn and the Justice Department that Sullivan gravely intruded on executive branch authority by allowing the planned hearing and inviting a presentation from a retired judge whom Sullivan appointed to argue against the government's motion to dismiss the case.

The majority opinion noted that the dissenters initially rejected Flynn’s request to have Sullivan’s case reassigned to another judge, but in Monday’s ruling said such a reassignment was merited.

"It is the trial judge’s conduct since the government’s May 2020 motion to dismiss, weighed in light of his earlier conduct, that delivers the coup de grâce to the last shred of the trial judge’s appearance of impartiality," Henderson wrote.

Borrowing a vivid phrase from Henry David Thoreau, she went on to describe Sullivan's decision to seek en banc review of the initial appeals court ruling "the trout in the milk." Although she voted against removing Sullivan from the case just a couple of months ago, in Monday's ruling she accused him of "glaring partiality."

Quora's What does the phrase "a trout in the milk" mean? explains:

The meaning is that although you did not see the dairy farmer do it, he most probably dipped the milk pail in the stream to water down the product. It’s not direct evidence but a very strong circumstantial case.

It is attributed as follows: "Some circumstantial evidence is very strong, as when you find a trout in the milk. ‘ (Henry David Thoreau)

I sometimes have trouble parsing analogies, and it's especially challenging when the topic involves carefully written legal opinions and potentially political motives of federal judges. So I'd like to ask:

Question: What exactly is the "Trout" in this D.C. Circuit Court of Appeals opinion? Is it the other opinion in toto or something specific within it, or in fact something else? Does the opinion suggest that the judge has a political motive?

Answer 1

The Thoreau analogy points to the idea that some pieces of circumstantial evidence are more convincing or robust than others. Following the analogy, there are a number of pieces of circumstantial evidence that might suggest a dairy farmer is watering down his milk. For example, the milk might have a funny taste; it might have too thin a consistency; it might not look 'milky' enough; then one might start to suspect that the farmer has dipped the milk pail in the local river to thin it out. But all those pieces of evidence are weak; the farmer could say one is imagining it all, and it would be difficult to argue otherwise. But if one finds a trout swimming in the milk, one can be fairly certain it didn't come from the cow, and the farmer would have a hard time brushing it off as mere imagination.

The context of the court case is a little convoluted. When the Justice department requested that the court drop the case against Michael Flynn, the trial judge in Flynn's case — Emmet Sullivan — denied the request so that hearings could be held on the matter. The Justice department immediately appealed to the District of Columbia Circuit Court of Appeals, where a three-judge panel overruled Sullivan 2-1, instructing that the case be dropped. Judge Sullivan then requested an en banc review — a review of the case by all eight Circuit Court judges on the bench — and this review supported Sullivan's position 8-2, nullifying the panel's decision.

Needless to say, the '2' in both cases were the same two Circuit Court judges: W. Bush appointee Karen Henderson and Trump appointee Neomi Rao. Henderson was the one who used the analogy, arguing that Sullivan's rejection of the panel decision — which Henderson herself authored — and request for an en banc review was clear evidence (the trout in the milk) of Sullivan's political bias, and was sufficient grounds to have Sullivan removed from the case entirely. The majority disagreed, assumedly because they didn't think there was anything all that 'fishy' about Sullivan's request.