Our exchange has us agreeing on the fundamentals--Congress' authority is limited to specific, "enumerated" powers; the original understanding of the Constitution was that courts would keep Congress within those limits; and courts today should continue to do so. Thus, you presumably do not subscribe to the view, expressed in the Supreme Court's 1985 Garcia case, that Congress' intrusions on state sovereignty cannot effectively be policed by the courts, and Congress must be left to be its own keeper.
You do express skepticism over whether "the court's effort to take seriously constitutional limits on Congress' power can be reconciled with the court's effort to take seriously a jurisprudence of original understanding." But it turns out that you mean the opposite of what this statement suggests--the court's recent concern to reassert limits on congressional power is consistent with, and indeed dictated by, the original understanding of the Constitution. You just don't think the court's "originalists" went far enough.
I will do my best to defend the concededly balanced approach of Chief Justice Rehnquist and Justices Scalia and Thomas.
Actually, the defense is simple: Your critique wholly fails to account for staredecisis, or respect for precedent. If the court's originalists in the Lopez case hesitated to return entirely to the original understanding of the Commerce Clause, they did so because they recognized that the country's reliance on the court's 60-year-old departure from the original understanding calls for great caution before reverting wholesale to that prior understanding. Justices who value originalism do not, as you imagine, begin anew in each case, selecting from among competing "visions" of constitutional meaning associated with different historical figures and times--Madison, Story, "pre-New Deal." Rather, the Constitution's original meaning is by definition its meaning at the time of origin, but there are occasions when court and country are already well down the road of an interpretation not wholly faithful to that meaning: In such instances, the originalist may determine to leave prior holdings undisturbed but to decide the case before him in a manner that departs no further from the original understanding, and that even--to the extent possible while giving precedent its due--reorients the court toward the Constitution's original meaning. This, I think, is a fair characterization of Lopez, where what you agree was the correct result was reached simply by distinguishing activities--like possessing a gun near a school--that are not "commercial" in even the broadest sense of the word.
Your second beef is with the court's decision in the Brady Bill case, but your argument seems to me no more than a quibble. You describe the case as "awkward for originalists," but au contraire: It's an originalist's dream, with majority and dissent virtually stipulating that the original understanding will be central to the outcome. You happen to find the dissent's explication of the original understanding more persuasive, but even if you're right (I say you're not), this has no methodological implication for originalism or congressional power beyond the case at hand. I note that you had to retreat from your initial claim that the case marked a reversal in method by Justice Scalia--he never "conceded" that the evidence in the Brady case was ambiguous. (Nor did I "concede" that he changed methods in the case, as you now claim.) You're also wrong that the majority did not consider constitutional text in the Brady Bill case: It devoted an entire section to Article II, and relied also on the 10th Amendment and decisions interpreting it--precedent that you again ignore.
So Jeff, let's put your claim about the Brady case aside and return to Lopez and the Commerce Clause: You agree that Lopez was rightly decided, but think that to be consistent with originalism, the majority should have gone further. Would you have? If so, how far? And if not, by what theory of constitutional interpretation was Lopez right?