Larry Lessig has a must-read post in his blog about the decision-making in Eldred v. Ashcroft (decided Wednesday, 7-2 in favor of the respondent).
As a good political scientist, I probably should point out that Larry's search for principle on the court is perhaps overly optimistic; the Spaeth attitudinal model suggests that the conservatives on the court would side with big business — and a Republican administration filing a supportive brief — regardless of principle. In terms of attitudinal signals, the plaintiffs' argument was sunk by the predominantly leftist amici. (Of course, being a good law professor, Larry probably doesn't buy the attitudinal model.)
Having said that, like Larry I can't reconcile Eldred with Lopez (a case that I believe was correctly decided on the merits), and I agree that the majority should at least have made an effort to do so; the point of having a “limited” government is that the limits must be meaningful, no matter what enumerated powers we're talking about. On that principle alone, the majority decided Eldred wrongly.
Glenn Reynolds makes much the same point (at least, one similar to mine) in his latest piece for MSNBC.com.