We hold, first, that the Act does not encroach upon the Appointment power because, in view of the [Securities and Exchange] Commission's comprehensive control of the [Public Company Accounting Oversight] Board, Board members are subject to direction and supervision of the Commission and thus are inferior officers not required to be appointed by the President. Second, we hold that the for-cause limitations on the Commission's power to remove Board members and the President's power to remove Commissioners do not strip the President of sufficient power to influence the Board and thus do not contravene separation of powers, as that principle embraces independent agencies like the Commission and their exercise of broad authority over their subordinates. Accordingly, we affirm the grant of summary judgment to the Board and the United States.