Senator Arlen Specter's testy interrogation of Judge John G. Roberts Jr. on the Supreme Court's treatment of Congress may well have left viewers scratching their heads on Wednesday morning, with cryptic references to the "congruence and proportionality test" and to unfamiliar case names like "Lane and Hibbs."

But the line of questioning that Mr. Specter, the Pennsylvania Republican who is Judiciary Committee chairman, chose to pursue offered a window on the increasingly troubled relationship between the court and Congress, as well as on one of the most consequential developments of the Rehnquist court's later years.