>Not constitution … legislated.
Article I, Section 1:
"All legislative Powers herein granted shall be vested in a Congress of the United States, which shall consist of a Senate and House of Representatives."
Article II, Section 2, Clause 2:
"… but the Congress may by Law vest the Appointment of such inferior Officers, as they think proper, in the President alone, in the Courts of Law, or in the Heads of Departments."
The Appointments Clause supplies the method of appointment for certain specified officials, but also for other [o]fficers whose positions are established by [l]aw. Although principal officers must be nominated by the President and confirmed by the Senate, Congress may by [l]aw place the appointing power for inferior officers with the President alone, a department head, or a court. As this section will explain, the Supreme Court has recognized Congress’s discretion to establish a wide variety of governmental entities in the Executive, Legislative, and Judicial Branches.
https://constitution.congress.gov/browse/essay/artII-S2-C2-3-6/ALDE_00000012/