#TrumpVAnderson First off, I don't think anything today swayed the Justices' opinions (as is standard for oral hearings). At the end of the day, I listened in to hear what the Justices cared about by what questions they asked, because I want to predict the ideological splits. Here are my clearest takeaways (some Justices omitted because my opinions on them are murkier, maybe because they didn't ask enough questions or because I couldn't tell who was speaking)
KBJ and Kagan seem to be taking similar stances on states' authority, with Sotomayor tentatively there if the two are willing to cabin that position to holding that Colorado's decision should only apply to Colorado.
Thomas wants to law-and-order this on Constitutional authorization grounds and keep Trump on the Colorado ballot. I'm not surprised given his reluctance to ever give weight to history behind the Fourteenth Amendment (that view puts him on the opposite side of the line to KBJ for a more specific reason than just political alignment).
Roberts seems the most well-informed on the debate as a whole. His use of that knowledge is concerning, because he's clearly got a view for how he'd write the majority (only applying the Fourteenth Amendment's Section 3, disregard any other constitutional provision's grant of authority or analogous treatment) and was only permitting Mr. Murray to argue along those lines.
One argument I think is particularly easy to follow (or at least rings closer to normal con law) is the debate around freedom of voters. If the voting population wants to elect someone, would a decision for Colorado effectively disenfranchise them? Of course, see Mr. Murray's legendary assertion that what Trump did was attempt to disenfranchise the entire nation.