This article from Lawfare is making the point that the Executive branch certainly seems to be lying to the Supreme Court, in telling it that the countries which were chosen for the travel ban were specifically lax in their security measures:
Will the Court ignore that possibility unless the other side can demonstrate some better evidence to that point?
If the Court believes the Executive branch to be lying to them, but believes that the Executive branch should be free to do as it will, regardless of the security measures of the specified countries, would the lie likely have any effect on their decision?
Lying to the court contains two different problems: the ethical violation and the effect on the factual dispute.
As for the factual dispute, the case is before the Supreme Court on appeal from a preliminary injunction. So the proceedings are not supposed to be about the facts so much as they are about how the law will apply if the facts shake out in favor of the plaintiffs. But the Supreme Court gets to do whatever it wants. And they frequently ignore the procedural posture of the case and get into all kinds of facts that are not in the record. But in theory, if they think a particular fact is both important and in reasonable dispute, then they are not supposed to deny relief to plaintiffs based on that fact.
As for the ethical breach, it would be very unlikely to affect the merits if it wasn’t factually relevant to their conclusion. Even if they concluded that they had been lied to, the normal solution is some sanction other than an adverse ruling on the merits. They would likely refer the matter to disciplinary investigation.
For what it’s worth, I’d be okay with the executive branch spending a night in jail for contempt.
Sell copies of the mug shots for ten bucks each to fund social security for the next ten years.
The large letter “L” tattooed on the forehead of said executive branch just got more obvious, that’s all.