The 2AM ruling last Saturday morning was astonishing, apparently without any precedent in the SC's history. There were three aspects that are so irregular as to indicate that Robert suddenly realized he could quite literally be facing the de facto end of the court. These aspects are:
1) It happened in the middle of the night. It was brought to the court in the early evening Friday as media reports showed that Trump had every intention of making another rendition flight in a matter of hours, in direct defiance of the previous SCOTUS order. Taking the case on such short notice is mildly unusual. But normally, there would be a stay and the court would get back to that days or weeks later. Why not issue a stay and be done with it? Well, as I understand it, Alito would be the one to initiate that action and he refused. So Roberts faced a choice of losing the court or overriding Alito. He made his choice, obviously, but it took a few hours of midnight oil to get everybody (save Alito and Thomas) lined up. And this means that Roberts had to convince 3 other GOP appointees that either they went with Roberts or else the court was effectively dissolved.
2) Roberts was pissed. There were about 6 hours when Alito could have written his dissent. Instead Alito just tried to stonewall and delay. So Roberts did the power move of saying (basically) "I don't give a F what Brother Alito is up to. I am not waiting for him to write some bullshit. And I don't have to wait for Thomas because he is functionally illiterate anyway. We are moving now. Alito can write his book report later if he wants to." This will leave a lasting gap between the Roberts 4 and Alito/Thomas. It was probably developing this way already, and this was the straw that broke the camel's back. So the hopeful sign is that maybe the Roberts 4 will be more reasonable now that they realize the danger they are in. I'm not saying they will behave completely differently, but the Roberts 4 may be more likely to work with the Dem 3 than Alito/Thomas on some future decisions.
3) They sent the issue back to -- THEMSELVES. That is highly irregular. The normal course is to send it back to the lower court with instructions. But Roberts now must realize that the 5th Circuit is as corrupt as Thomas and Alito, so he did not give them the chance to work around the SC. Roberts issued a stay until the full SCOTUS issues a ruling on the use of the 19th century law.
This is a huge moment for the SCOTUS. Let's hope that the Roberts 4 have learned something about the danger of the fascism they have been enabling.