In Article 2, Section 2 of the Constitution of the United States, it discusses the role of the president as Commander in Chief of the U.S. military forces. The current president, even after he assumes the role of president and takes office, does not actually assume control of the military until "called into service" by the Congress. According to Article 1, Section 8, only Congress can decide to declare war on another country. Until such time as they call on the president, he actually has no active role in the military proceedings of the country. However, many presidents have historically sent troops to war without actually formally declaring war. Therefore, presidents have often ignored or bypassed the rules intended by the authors of the Constitution.
This angered many legislators, so under the War Powers Resolution of 1973, it was decided that presidents could only send troops to battle in the case of "a national emergency created by attack upon the United States, its territories or possessions, or its armed forces." The resolution also specified that the president must withdraw troops sixty to ninety days after beginning combat in a foreign territory, unless Congress authorized the continuation of troops there. The legislature does not fully address how conflicts will be ended, however.
Legal experts and constitutional scholars agree that although the Constitution originally handed Congress the power to make and end wars, it only intended for the president to hold the power to wage war effectively, under whatever circumstances war was declared. While Congress was intended to have the sole power to formally end a war, once the commander in chief is authorized to take control of the troops, they must actively work together to make an end to war happen. This contributes to the balance of power that is necessary to both check the power of the president as well as the power of Congress.
Congress may set limits for troop withdrawal, as in the case of the deployment of troops in 1983 to Lebanon on a peacekeeping mission. That power was never tested, as they withdrew the troops early after a suicide bombing occurred in the area. To this day, U.S. presidents have loosely acknowledged the agreed upon time limits for troop withdrawal, but not in all cases. In fact, the president may refuse to withdraw troops if he does not agree with the limit imposed, and Congress may only stop him from doing so by passing a law that commands him to do so—a law that is subject to presidential veto. He or she would only need 34 senators to back him, and as most presidents can achieve this easily, he would ultimately hold the power in deciding when the war is officially over.