It is a close contest which recent assertion of executive authority crowns the rest, but the Administration’s potential skirting of the Senate’s treaty power in negotiating an international agreement on climate change ranks high in the running. The Constitution’s explicit partnering of the Presidency and the Senate in binding the nation in global agreements, combined with the two-thirds majority needed in the upper chamber of Congress to affirm them, points to the unique dangers of cutting one institution out of the process. President Obama is not the first to do this. Chief magistrates have long invoked “executive agreements” to sidestep the ratification process, and President Bush used one that looked every inch a treaty to conclude a major status-of-forces arrangement with the then-Prime Minister of Iraq. But doing so on a matter of landmark and sharply contested domestic policy marks another step in the steady inward turn of the imperial presidency.

The two most relevant numbers of The Federalist on this topic—64 and 75—identify several advantages of a blended role for the President and Senate in concluding treaties, each of which is vitiated by the use of executive agreements. One is the familiarity with the complex and, crucially, local affairs of an extensive republic that a legislative body offers. Another is the difficulty of corrupting a legislative body as opposed to an individual. A third is the wide perspective and stable judgment a Senate adds to that of a single leader who is more susceptible to misjudgment or caprice.

In Federalist 64, Publius observes:

In proportion as the United States assume a national form, and a national character, so will the good of the whole be more and more an object of attention; and the government must be a weak one indeed, if it should forget, that the good of the whole can only be promoted by advancing the good of each of the parts or members which compose the whole.

Presidents can disregard parts. A Senate requiring a two-thirds majority cannot. One contribution the Senate thus makes is attachment to local interests and an assurance of their representation. Even a President intending to represent the whole does not know local interests like Senators elected to represent them.

A multifarious Senate, according to Publius, is also incorruptible in comparison with a single President. Federalist 75 is unwilling to commit the treaty power to a single magistrate who would be more easily corrupted than an entire legislative body. “The history of human conduct does not warrant that exalted opinion of human virtue, which would make it wise in a nation to commit interests of so delicate and momentous a kind, as those which concern its intercourse with the rest of the world, to the sole disposal of a magistrate created and circumstanced as would be a president of the United States.”

Publius’ point is that a President, serving temporarily and thus less identifying him or herself with the country than might a king or queen, could find personal and national interests at odds. Under the glare of modern media and relentless transparency, it is difficult to imagine literal corruption in the sense of a foreign government paying a President off, which appears to be Publius’ immediate concern. But the corruption of ambition—especially the ambition to write a rapid and enduring legacy for the history books in the short space of four or eight years—might well counsel shortcuts around the laborious process of ratification that bind the country to agreements. Executive agreements serve Presidential interests; the ratification process does not.

A single individual is also more liable to personal caprice or misjudgment than a body, especially one constituted like the Senate—comprised of older individuals serving for longer terms, rotated in staggered terms. Federalist 64 thus praises the commitment of the ratification power to a body, the Senate, that does not go entirely in and out of existence at a single moment, as Administrations no less than Houses of Representatives do. By this means, “uniformity and order, as well as a constant succession of official information, will be preserved.”

The involvement of the Senate also makes agreements themselves more stable—and thus more attractive to foreign governments—because it is more difficult for the President to abrogate them at will. Publius remarks, again thinking of the House in logic that applies to executive agreements: “[A] treaty is only another name for a bargain, and … it would be impossible to find a nation who would make any bargain with us that should be binding on them absolutely, but on us only so long and so far as we may think it proper to be bound by it.” Yet agreements entered into unilaterally by executives—like policies imposed unilaterally by executives—are just as easily reversed by their successors. Nations that get into the habit of being so deserted are less likely to enter into serious negotiations on serious topics, even through the serious means of actual treaties.

Publius also notes in Federalist 75 that treaties partake partly of legislative and partly of executive character. They are, he says, more properly likened to contracts. Excising the Senate from the process may at first appear to be an attempt to proclaim them entirely executive. It is not. It is instead another attempt to establish the President as a legislator: the chief policymaker by virtue of national election.

The long-term prognosis of that practice is rapidly fluctuating policies, imposed by narrow plebiscitary majorities insensitive to minority views. Who occupies the majority at any transient moment is immaterial. The point is not climate change, or immigration policy, or the policies a Republican President is virtually certain to attempt to use the same powers, once established, to pursue. The point is that the separation of powers is the bedrock of constitutionalism. Publius—see Federalist 47—had a phrase for the combination of powers that a swollen Presidency of either party threatens: “the very definition of tyranny.”