A reader asked me to comment on this case, which has garnered a lot of media coverage, mostly of uneven quality.  As my colleague elsewhere aptly put it: "Is the Court's decision the end of the world, or will we get through it?"

The short answer:  too soon to say!  It may not be that significant, or it may be very significant.  SCOTUS stayed its own decision for 30 days, on remand to the lower courts.  What the lower courts do (since the decision leaves open many possibilities) and how SCOTUS responds, if at all, will determine what comes next.  Trump is obviously a lawless gangster, but note that the decision also applies to the "Supreme Court of Amarillo" (as I like to call it), where the lone federal judge in the district in that part of Texas, is a far right anti-abortion zealot,  who used universal injunctions to bar distribution of medicines that induced abortions.  As Trump appoints awful federal judges, the SCOTUS opinion may look prescient.  Put differently, evaluating this decision with only the monster child in mind may be a mistake (or it may not, as Professor Mike Dorf plausibly argues).

Some abbreviated background:  "equitable" remedies, like injunctions, are, historically, remedies that were not provided by for law and were afforded by special courts of equity in England (the US is an inheritor of the English common-law system:  in a common-law system, courts develop the law, as do legislatures).  A court will not "enjoin" (i.e., stop) conduct unless the party complaining of the conduct is likely to prevail on the merits of their objection and money damages will not suffice to compensate for the harm caused by the unlawful conduct.  (It's more complex than this, but this should suffice for purposes here.)

The question before SCOTUS was whether the Judiciary Act of 1789, the statutory authority under which federal courts award equitable relief, allowed judges to bar likely unlawful conduct by the government beyond the parties before the court, i.e., to bar enforcement of the law against anyone.  The majority opinion by Justice Barrett, argued that the answer was negative, based on the historical evidence.  I think this argument is probably correct, but my general view about "originalist" or "historical" arguments is:  who cares?  Why should we bound by long dead people whom none of us voted for, who are wildly unrepresentative, and had, at best, uneven judgment?  The answer can't be because otherwise there is no constraint on judges (even assuming, contrary to the evidence, that originalism actually constrains judges):   there are lots of way to impose constraints on judges without binding the polity to the practices of 1789 or before (e.g., binding precedent, not to mention political backlash from the other branches).  So while I think the whole methodology is indefensible, I think, given the method, the decision was "legally sound."  (This is one reason all legal positivists think the legal correctness of a decision is one thing, and whether it is a good or sensible decision is another!)

But the decision left several rather important issues undecided, and that's why the import of the decision may (or may not) be minimal.  Here are the three most important.

First, states have standing to sue on behalf of their affected citizens–if the state wins an injunction, that applies to all residents of the state.  But some of the states in this case argued that it is far too difficult to determine who within its jurisdiction has birthright citizenship (since, of course, people move throughout the country), and therefore, only a nationwide injunction will afford adequate relief.  Will the lower courts endorse that argument?  Will SCOTUS let it stand?  That remains to be seen.  Even if SCOTUS does not allow a state to secure a nationwide injunctions, civilized states can still get injunctions for their citizens against the most egregious Trump misconduct–yet another reason why livign in a civilized state is increasingly important in the Benighted States of America.

Second, class actions–an action in which named plaintiffs represent a much larger, nationwide class of similarly affected parties–remain an option and, indeed, CASA, one of the original plaintiffs in this case, filed a class action shortly after the SCOTUS decisions.  There are challenges to certifying a nationwide class, but if the class is certified, then a nationwide injunction would be reqiured to provide relief.  (Whether SCOTUS lets the class certification stand remains to be seen as well.)

Third, parties can bring emergency petitions to SCOTUS, which has nationwide juridiction and so could issue such an injunction.  

If the U.S. survives Trump, and if SCOTUS permits some of the preceding ways of securing nationwide injunctions for egregiously unlawful government action (like the executive order on birthright citizenship), then it may be a good thing that some of the awful judges Trump has appointed and will appoint are deprived of the weapon of nationwide injunctions.  (As readers will know, Trump appointed Federalist Society approved judges, only to realize, too late, that most of them believed in the rule of law, and were not his henchmen.  Having soured on the Federalist Society, one can expect Trump to put forward increasingly awful judicial nominees, which the supine Senate will mostly confirm.)