Hamilton turns in Federalist No. 75 to the shared responsibility of the president and the Senate in making treaties with other nations–a subject already discussed by John Jay in No. 64. For such a passionate advocate of a strong executive, he makes what seems an interesting concession when he says this power “will be found to partake more of the legislative than of the executive character.” This was more than Jay said in an essay placed in the series on the Senate, and here Hamilton is in the midst of a series on the presidency. But if we read on we see that the power is of a mixed character, which frees us to think in practical terms about where best to place its operation. Hamilton marks the phrase just quoted with a comma, followed by this:

though it does not seem strictly to fall within the definition of either of them. The essence of the legislative authority is to enact laws, or in other words to prescribe rules for the regulation of the society. While the execution of the laws and the employment of the common strength, either for this purpose or for the common defence, seem to comprise all the functions of the executive magistrate. The power of making treaties is plainly neither the one nor the other.

Several times Hamilton seems on the brink of saying that the treaty power belongs to the sphere of what the English political philosopher John Locke called the “federative” power, the direction of foreign affairs in general, or as he puts it in chapter 12 of his Second Treatise of Government, “the power of war and peace, leagues and alliances, and all the transactions, with all persons and communities without the commonwealth.” Locke unites this federative power with the executive, “both of them requiring the force of the society for their exercise.”

Hamilton eschews such theoretical distractions, though, instead homing in on the practical issue of how diplomacy works, which alone explains the wisdom of making the president the primary actor in the treaty power:

To have entrusted the power of making treaties to the senate alone, would have been to relinquish the benefits of the constitutional agency of the president, in the conduct of foreign negotiations. It is true, that the senate would in that case have the option of employing him in this capacity; but they would also have the option of letting it alone; and pique or cabal might induce the latter rather than the former. Besides this, the ministerial servant of the senate could not be expected to enjoy the confidence and respect of foreign powers in the same degree with the constitutional representative of the nation; and of course would not be able to act with an equal degree of weight or efficacy.

Put the Senate wholly in charge of treaties, and it will find it necessary to entrust the negotiation of them to someone. The president, who will stand already at the head of a diplomatic corps that answers to him, is the natural choice. No other emissary sent by the Senate can bring the credibility of “the constitutional representative of the nation.”

In short, for these “agreements between sovereign and sovereign,” nothing will do but assigning the primary role to the officer who speaks for American sovereignty in our foreign relations in general.

(For explanation of this recurring feature, see here.)