Eugene makes a good point (below) about the way that Breyer’s and Scalia’s positions gives room to both liberal and conservatives to take a position seemingly at odds with their ideologies.
I would add that there is a way in which Breyer’s and Scalia’s votes are completely unsurprising: Scalia’s position is in line with his longtime formalism, and Breyer’s is consistent with his longtime pragmatism. The plurality opinion that Breyer joins is suffused with pragmatism. The plurality finds that the mushy Mathews v. Eldridge test applies (despite the fact that, according to Thomas’ dissent, none of the parties cited Mathews even once), and then engages in an ad hoc balancing process designed to make sure that Hamdi gets to challenge his detention but that the government is not unduly burdened.
Scalia, meanwhile, finds that the Constitution does not allow the government to hold a citizen without detaining him, unless it suspends the writ of habeas corpus. He finds that the Constitution and the common law defeat the government’s claims, so there is no role for a balancing test. His view is that this may not be the most efficient or pragmatic approach, but it is the one that the law provides. If people don’t like that, their representatives can change the law.
What’s interesting here is that this split is not as unusual as some might imagine. Yes, this court is split 5-4, along conservative/liberal lines, in many cases (think Bush v. Gore). But in some notable cases it has been split 5-4 along formalist/pragmatist lines. One of the biggest cases of the last few years is Apprendi v. New Jersey, in which the Supreme Court held that juries, not judges, must impose increases in penalties for a crime beyond the prescribed statutory maximum. That case was 5-4, with Stevens, Scalia, Souter, Thomas and Ginsburg posed against Rehnquist, O’Connor, Kennedy, and Breyer. The exact same lineup occurred in Blakely v. Washington, which came down last Thursday and imperils the federal sentencing guidelines. As for Hamdi, the reason that the five formalists (Scalia, Stevens, Souter, Thomas, Ginsburg) didn’t win is that one of them (Thomas) found his formalism taking him in the opposite direction — he alone adopted the government’s position, across the board.
I’m not claiming that formalism v. pragmatism will always (or even often) trump other fault lines, but I do think it’s interesting that this split has arisen in such big cases as Apprendi and Hamdi.