Opinion of Thomas, J.
would render “as nugatory, all [the States'] deliberations on the Constitution” and effectively vest Congress with “general authority to legislate on every subject.” 3 id., at 308–310 (1792) (emphasis deleted). Each of these comments presumed that the word “proper” imposed a jurisdictional limit on congressional activity.
This evidence makes sense in light of the Framers' efforts to ensure a separation of powers, reinforced by checks and balances, as “practical and real protectio[n] for individual liberty in the new Constitution.” Perez v. Mortgage Bankers Assn., 575 U. S. 92, 118 (2015) (Thomas, J., concurring in judgment). If Congress could rely on the Necessary and Proper Clause to exercise power expressly allocated to the other branches or to prevent the exercise of such power by other branches, it could undermine the constitutional allocation of powers.
That the evidence thus points to a definition of “proper” that protects the separation of powers does not fully explain the way that the “proper” requirement operates when Congress seeks to facilitate the exercise of a power allocated to another branch. I can see two potential mechanisms, either or both of which may accurately reflect the original understanding of the Clause. First, a law could be “improper” if it purports to direct another branch's exercise of its power. See Calabresi & Prakash, The President's Power To Execute the Laws, 104 Yale L. J. 541, 591 (1994) (“[T]he Clause . . . does [not] allow Congress to tell constitutionally empowered actors how they can implement their exclusive powers”). Second, a law could be “improper” if it takes one of those actions and the branch to which the power is allocated objects to the action. See Prakash & Ramsey 255–256 (“Congress has the general power to legislate in support of the President's foreign policy goals. But . . . [s]ince it is derivative of the President's power, it must be exercised in coordination with, and not in opposition to, the President”).
