What does the Constitution say? - The Constitution says that the President can act as commander-in-chief, and negotiate treaties. These are checked by Congress, but are not foolproof, for example, Congress has not declared war since 1941, and the ‘power of the purse’ has proved ineffective if troops are already abroad, such as the Iraq war in 2003. The Constitution also lets the President appoint members to the executive branch who may influence foreign policy, such as national security advisor, secretary of state, or secretary of defense. Ambassadors to the EU, NATO, or the UN also help. These appointments, however, are subject to Senate confirmation, apart from national security advisor.