shall be held to answer” for a serious crime “unless on a presentment or indictment of a Grand Jury”). “[T]he whole theory of [the grand jury’s] function is that it belongs to no branch of the institutional government, serving as a kind of buffer or referee between the Government and the people,” United States v. Williams, 504 U.S. 36, 47 (1992), “pledged to indict no one because of prejudice and to free no one because of special favor.” Costello v. United States, 350 U.S. 359, 362 (1956). If the grand jury were not protected against corrupt interference from all persons, its function as an independent charging body would be thwarted. And an impartial grand jury investigation to determine whether probable cause exists to indict is vital to the criminal justice process. * * * The final step in the constitutional balancing process is to assess whether the separation-of-powers doctrine permits Congress to take action within its constitutional authority notwithstanding the potential impact on Article II functions. See Administrator of General Services, 433 U.S. at 443; see also Morrison, 487 U.S. at 691-693, 695-696; United States v. Nixon, 418 U.S. at 711-712. In the case of the obstruction-of-justice statutes, our assessment of the weighing of interests leads us to conclude that Congress has the authority to impose the limited restrictions contained in those statutes on the President’s official conduct to protect the integrity of important functions of other branches of government. A general ban on corrupt action does not unduly intrude on the President’s responsibility to “take Care that the Laws be faithfully executed.” U.S. CONST. 1090 ART II, §§ 3. To the contrary, the concept of “faithful execution” connotes the use of power in the interest of the public, not in the office holder’s personal interests. See 1 Samuel Johnson, A Dictionary of the English Language 763 (1755) (“faithfully” def. 3: “[w]ith strict adherence to duty and allegiance”). And immunizing the President from the generally applicable criminal prohibition against corrupt obstruction of official proceedings would seriously impair Congress’s power to enact laws “to promote objectives within [its] constitutional authority,” Administrator of General Services, 433 U.S. at 425—i.e., protecting the integrity of its own proceedings and the proceedings of Article III courts and grand juries.