I don’t see what you’re talking about.
The original comment quite explicitly introduced the comparison.
The idea of the Justice Department “going back” to being independent is a direct assertion that it used to be independent, and now no longer is. The comparison is right there in the statement.
@Sam_Stone then attacked that explicit comparison to how things used to be, by bringing up evidence of the previous administration. I wouldn’t actually call the evidence then cited very good. It would have been better to cite multiple administrations, as he later did.
If the original comment had been: “I hope the Justice Department under the next administration isn’t total subservient shit like it’s been under Trump”, then that’s a different comment, not making any explicit reference to the quality of any previous administration.
I think Sam_Stone’s comment would have been a tu quoque in that case, given my understanding of the term.
But if a comment of “Things used to be better, and I hope they will be again” is answered with “Things did not used to be better”, then I don’t see at all how that is supposed to fit the fallacy. Not remotely. This is true regardless of the quality of the evidence provided about things not having been better.