In thinking about the implications of Trump v. United States for the general issue of conceptualizing emergency powers under the US Constitution, which might be the topic of a subsequent post, I started to wonder about textualism and linguistic drift. The "domestic Violence" clause is by now a standard example of why the Constitution has to resist linguistic drift (though in my view syntax alone would be sufficient in this example: how could the United States protect states against what we now think of as domestic violence?). Similarly with Jack Balkin's "what part of Republican form of government don't you understand?" example (though there too syntax is sufficient--his joke referred to Bush v. Gore, which didn't involved guaranteeing a republican form of government for each state, though I suppose you can apply it to the Court's partisan gerrymandering decision).
What are we to make of the term "invasion," which occurs three times in the Constitution (in the habeas-suspension clause, in the Compact Clause [as "actually invaded"], and in Article IV)? The term has its place in contemporary conservative discourse, which characterizes what's happening at the US southern border as an invasion. One can imagine a Trump administration suspending habeas in connection with those who cross the border without authorization. Conservatives might assert that Article IV places a duty on the United States to protect states against invasions (one of which is occurring) and that the President's failure to do so provides the basis for impeaching him for failing to take care that the laws be faithfully executed. (At least one impeachment resolution invokes this theory.)
Is this an example of (a) impermissible linguistic drift or (b) permissible specification of vague constitutional terms within the bounds of reasonable interpretive flexibility? I did some quick and dirty research (this is a blog post, after all), and came up with this. The 1785 edition of Samuel Johnson's dictionary defines "invasion" as "a hostile entrance upon the rights or possessions of another," and provides four illustrations, of which two involve invasions by organized military forces of hostile nations (and the other two of which seem to me metaphorical). Noah Webster's 1828 dictionary's first definition is: "a hostile entrance into the possessions of another; particularly, the entrance of a hostile army into a country for the purpose of conquest or plunder, or the attack of a military force. The north of England and south of Scotland were for centuries subject to invasion each from the other. The invasion of England by William the Norman was in 1066."
My real puzzle isn't about "the" answer to the question posed in the preceding paragraph. (About 15 years ago I suggested, in passing, that the September 11 attacks could plausibly be characterized as an invasion for purposes of habeas suspension, thus assuming that organized attacks by a hostile non-state actor could count as an invasion. What about the ISIS-influenced attack by a single individual at Fort Hood years later?) The puzzle is about how to think about figuring out the answer. My guess is that there's a sophisticated literature in the philosophy of language about the distinction the question draws--and my guess is that that literature, though perhaps a tempting source for legal academics, is likely to be quite unhelpful.
Anyhow, a suggestion for a law review article or student note? For a first stab, see this, from what Wikipedia describes as a conservative think tank. (And perhaps a preliminary to a post on emergency powers.)