Jumping back in for the first time in months, so please forgive me if someone actually said something about this already (other than, "what does this mean?!").
There are two parts to Judge Kathryn Kimball
Mizelle's decision today:
1) The CDC did not have sufficient authorization from Congress to issue such a sweeping mask mandate on federally-regulated transportation in January 2021 following President Biden's Executive Order (that is, the regulation was written sloppily); and,
2) In issuing its mask mandate, the CDC failed to show why it should not follow the regular procedural requirements of "notice and comment" under the Administrative Procedures Act - the basic rule that says federal agencies must seek outside comments on most proposed agency regulations (that is, the rule was issued in haste for no good reason).
As discussed repeatedly here over the course of the pandemic, at the start of an emergency, courts generally give agencies wide deference (leeway to act), including pandemics, without following lots of procedural rules when there isn't a lot of information available about the problem and/or no real remedies available. Over time, as we learn more about both the problems and the remedies, those procedural and substantive limits flow back into force, so that courts will require more and more precision in governmental regulation. At least that is the process that has been followed repeatedly throughout our history, including most recently during the pandemic.
Judge Mizelle's decision follows in that same pattern. She found, basically that the CDC acted too quickly and too broadly after President Biden's Executive Order. On both parts of her decision, however, she has written on the extreme edge of precision in that form of review (IOW, she's applying as strict an interpretation of those rules as she can find in both current and prior examples), but that does not make her decision any less effective or reasonable.
For example, on part one (the CDC's authority to hand down sweeping mandates), Judge Mizelle, in the final analysis, follows carefully the new versions of the "major questions" doctrine: agencies cannot issue regulations making sweeping rules that govern many sections of American life or many people unless Congress has clearly written the agency's governing law to give it that specific power. "Major questions" require more specific authorization than the tweaks and clarifications ordinarily the fodder of government regulations. Basic rule: the bigger the government action, the more precise the legislative authorization must be. We're more likely to see that sort of sweeping "carpet bombing" regulation at the early stages of emergencies like pandemics; the requirements for precision follow inevitably, and that's what this decision was. Too broadly written, too hastily. Not enough precision, at least partly because the agency narrowly followed the Executive Order rather than the APA's requirement to hear from all sides.
Given her strong findings on both these parts, it's no surprise that she issued a powerful order - vacating (voiding) the regulation and remanding (returning it) to the CDC to try better on both fronts. Again, she didn't have to do it that way, especially given that the mandate expires in a couple of weeks, but given the trend in higher court opinions recently, she was well within her jurisdiction to do that. Her assertion of a national injunction, however, was overbroad, and she knew it. Slip op. at 55.
