I'll give rare kudos to Slate here, where writer Mark Joseph Stern went into a lot more detail than the MSM in explaining exactly why Judge Colleen Kollar-Kotelly issued a ruling halting President Trump's ban on transgenders serving in the military. Stern clearly thinks her reasoning is solid. But I think it's useful to those who believe the president had the authority to issue the ban, precisely because Judge Kollar-Kotelly's argument is so lacking in actual legal reasoning.
What follows is mostly Stern's summary of her argument, with the italicized portion coming from the judge itself: