Justin Yang is a junior at the University of Pennsylvania studying Politics, Philosophy, and Economics.
After President Trump announced he was planning to pull the United States out of the Paris climate accord, several states announced that they would defy the president and adhere to the accord themselves. In particular, California has tried to step up and fill the void the United States has left behind, meeting and striking climate deals with foreign governments like China.  In addition, a New York Times report revealed that governors are increasingly conducting the diplomacy they believe the Trump administration is neglecting: they are going abroad and meeting with foreign leaders, assuring them of America’s stance on climate change and trade.  All of these developments raise an interesting question: can a state conduct what appears to be foreign policy without the federal government?
The Constitution does not explicitly grant the power to conduct foreign policy in general to any particular institution, but it gives to the President power to negotiate treaties, to lead the armed forces, and to receive foreign ambassadors.  It also grants Congress the power to approve of treaties, the military budget, and the President’s nominee for the Secretary of State, as well as the power to regulate commerce with foreign nations and to declare war.  All this seems to imply that the federal government has the exclusive right to conduct foreign policy, a view that the Supreme Court has long held. In 1840, the Court held in Holmes v. Jennison that “it was one of the main objects of the constitution to make us, so far as regarded our foreign relations, one people, and one nation; and to cut off all communications between foreign governments, and the several state authorities.”