What is the effect of Rule 12 on the "motion in bar"?

15 Rule 12, dealing with pre-trial motions, was the subject of great debate in United States v. Mersky, 361 U.S. 431, 80 S.Ct. 459, 4 L.Ed.2d 423 (1960). There, Mr. Justice Brennan in his concurring opinion, 361 U.S. at 441, 80 S.Ct. 459, 4 L.Ed.2d 423, and Mr. Justice Stewart in his dissent, 361 U.S. at 453, 80 S.Ct. 459, 4 L.Ed.2d 423, joined issue on the effect of Rule 12 on the historic "motion in bar." Mr. Justice Brennan argued that Rule 12 swept away the common law motion in bar in favor of a broader rule. Mr. Justice Stewart argued that Rule 12 merely carried forward the existing federal law relating to a motion in bar which itself was somewhat broader than its common law predecessor. But both Justices focused on what they found to be the proper interpretation of the Rule, and neither recognized any inherent power to go beyond whatever the proper interpretation was found to be.