Here’s what I take as the crux of today’s majority decision and one which I suspect may come up again in subsequent decisions given President Trump’s behavior …
For our purposes today, we assume that we may look behind the face of the Proclamation to the extent of applying rational basis review. That standard of review considers whether the entry policy is plausibly related to the Government’s stated objective to protect the country and improve vetting processes. See Railroad Retirement Bd. v. Fritz, 449 U. S. 166, 179 (1980). As a result, we may consider plaintiffs’ extrinsic evidence, but will uphold the policy so long as it can reasonably be understood to result from a justification independent of unconstitutional grounds.5
The point here is that it doesn’t matter if the President says things that suggest he took the action for a bad/unconstitutional reason. What matters is whether the policy can “reasonably be understood” as the product of a legitimate reasoning. The standard doesn’t seem absolute. They say they may consider “extrinsic evidence”, i.e., evidence beyond the narrow facts of the case – what the order says, its direct effects, etc. But the standard they will use is whether the action can be reasonably understood as the product of a legitimate reason – even if there’s evidence in the President’s mouthing off that suggests otherwise.
So to get down to specifics, without the context of the President’s words you can look at this order and you can make an argument that it’s an effort to block entry from countries with terrorism problems or from unfriendly countries. If that’s the case, that’s enough. As long as this is a reasonable interpretation absent the context, we will set aside the context, i.e., what the President said at rallies or on Twitter.
There is a touch of ambiguity here. I could read these words to mean that the “extrinsic evidence” could be so overwhelming that it made thinking the decision stemmed from anything else than unconstitutional grounds ‘unreasonable’. Still, I think the basic point is clear, both in the result and the argument: the Court won’t get tripped up by interpretations of Trump’s rants and free associations. If the actions can reasonably be to result from legitimate justifications that will be the end of the analysis.