Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors, equal to the whole Number of Senators and Representatives to which the State may be entitled in the Congress: but no Senator or Representative, or Person holding an Office of Trust or Profit under the United States, shall be appointed an Elector.
U.S. Const., Art. II, § 1, Cl. 2
Yes, so it's a constitutional requirement. Which is another way of saying that what HRC is babbling about is of no import.