ture is more capable than the judiciary at saying "what the law is," would the Constitution still mandate judicial review?4
The supposed fact that legislators cannot restrain themselves under a written Constitution has relevance only because Marshall read the Constitution so as to raise the empirical issue. At the same time, Marshall probably would not have read the Constitution as raising this empirical issue if he had not already anticipated the answer. Marshall, it appears, found the fact normatively and used it rhetorically in the same way he used other external authority.5
The asserted facts, together with the other authority explicitly or implicitly relied upon, were combined in Marbury to establish the constitutional principle of judicial review. The "correctness" of Marbury depends on the correctness of the various premises of Marshall's argument, including the factual supposition regarding legislators' self-discipline. The only true test of the facts' import can come if the facts change, or they are demonstrated to be different than the Court supposed.6
In McGrain v. Daugherty, where the executive power was not at risk, the Taft Court gave a boost to legislative authority. There the Court resoundingly affirmed a broad implicit congressional power to investigate matters pertinent to possible legislation.7
The question in McGrain was whether the Senate exceeded its power under the Constitution when it compelled a private individual to appear before it or one of its committees and give testimony needed in directing an investigation of the Attorney General. Van Devanter found that the Constitution, Article 1, ?Sl and 8 provide invests Congress with 'all legislative powers' granted to the United States, and with
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