In a democracy governed by a constitution, like the United States, the president exerts his or her power within certain limits. One legal limit to political power at the domestic level is the separation of powers, something James Madison described as a means of preventing all power from becoming concentrated in the hands of the many, in the hands of the few or in the hands of one person. Another such limit is the legal recognition of the fundamental human rights that so define the U.S. Constitution and make explicit the right of the individual not to have to suffer from the demands of those in power. Donald Trump, during these first weeks of his presidency, has tested the limits of his power on the domestic level and dealt with criticism from American society opposing his administration’s policies. Trump has also been testing the outer limits of U.S. power.

It is true that the U.S. is a great power, but it is not self-sufficient; nor can it live in isolation. Instead, the U.S. participates within a world composed of other states, which, due to the manner in which international society functions, must navigate around the external limitations placed upon them by U.S. power. Under Trump, this has come to mean the exclusionary and self-described policy of “America First.”

International relations are not constrained by the principle of “everyone being at war with everyone,” as Hobbes spoke of, even if war remains an ever-present, limiting situation. In effect, due to their growing interdependence, states have been creating norms and institutions by mutual agreement, intended to govern their respective and reciprocal conduct. Said conduct is dictated by the general understanding that a common interest exists in maintaining these norms and institutions given that they give rise to coexistence and cooperation between states and societies in today’s globalized world.

International law is an expression of this reality, and among its functions in the context of the dynamics of collective, interstate coexistence, is the need to provide information on state actors’ probable behavior and to demonstrate an acceptable pattern of conduct. In this way, it establishes a theoretical framework regarding the external limits on the “rules of the game” within diplomacy.

There’s a reason that diplomacy, both at the bilateral and multilateral level, is an instrument of foreign policy, something that Trump has demonstrated little appreciation of, as reflected in his disregard of the State Department. States must be able to communicate and interact in an institutionalized manner. Diplomacy is dialogue, not solipsistic monologue; it opens up the possibility of learning the point of view of others, whether or not you want to accept them, and offers a way to search for common ground. As the British diplomat, Lord Strang, used to say, “In a world where war is everybody’s tragedy and nightmare, diplomacy is everybody’s business.”

It’s for this reason that the lack of diplomacy seen in Trump’s behavior is a legitimate concern in an unstable world whose yet indiscernible extremes are being influenced not only by wide-ranging emotions but pervasive tensions as well. It’s never a bad idea to remember how gestures and words together influence actions taken within the context of diplomacy or how words, to evoke Cecília Meireles, have an “unusual power” within them, as they have the ability to channel visions and boldness or, on the other hand, communicate anger, slander and defeat.

Trump’s actions, his exaggerations, his use of Twitter as a preferred method of incoherent communication and his willingness to affirm “alternative facts” each have consequences given the importance of the United States.

I’ll give you an example related to the World Trade Organization. The Vienna Convention on the Law of Treaties establishes that parties must uphold and comply in good faith with all treaties in effect. Trump, by affirming that he will aggressively defend American sovereignty in trade policy by only taking into account his own country’s laws, is placing non-compliance with assumed laws and obligations on the agenda. He thus undermines not only his country’s trustworthiness but also the good faith prevailing within international diplomatic relations.

The WTO, which replaced the General Agreement on Tariffs and Trade, constructed a multilateral trade system, whose mission is universal in nature, governed by norms that are an expression of parties’ reciprocal interest in cooperating, which also safeguards parties from the risks of unilateralist practices in international trade.

The benefit of the WTO is its norms and the observance of said norms. They exist in order to ensure the security and predictability of the expectations of the parties.

Trump’s statements, along with the document on trade policy he sent Congress regarding the possibility of the U.S. — unilaterally and in the face of WTO norms — raising new tariff and non-tariff barriers and not complying with decisions that arise from the WTO’s system for handling disputes, undermine confidence in the multilateral trade system. As this system is based on reciprocity of interests and the interplay of mutual claims and tolerance, of which the U.S. internationalist Myres S. McDougal once spoke, the rise of extreme stances like that of “America First” could, as the qualified and recently elected WTO Director-General Roberto Azevêdo observed, “cause a chain reaction with devastating effects for everyone.”

International trade has become a scapegoat in the United States as a result of nationalist and populist elements — although not exclusively because of them — for problems whose root cause is not trade but rather changes that have occurred in recent times within the productive sector. Thus, as Azevêdo pointed out, “Closing off countries to trade is not the solution.” Azevêdo was recalling the lessons learned from the economic crisis of the 1930s when trade barriers ended up impacting two-thirds of global trade, something that exacerbated tensions and helped lay the groundwork for World War II.

It was the horror of war that inspired the creation of a world order, of which the WTO has been an integral part, that would be more conducive to cooperation than to conflicts. The WTO itself is at risk of feeling the ripple effects from Trump as he tests the limits of his country’s external power.

The author is professor emeritus of international relations at the University of São Paulo and was the former minister of foreign relations under Brazilian President Fernando Henrique Cardoso.