Under what authority can the President act unilaterally in military affairs?

The President's authority to act unilaterally in military affairs is primarily derived from the role of Commander-in-Chief, as specified in Article II of the U.S. Constitution. This role grants the President the power to direct military operations and make decisions regarding the deployment of armed forces without needing prior approval from Congress. The President can respond swiftly to military threats and execute strategies that are deemed necessary for national security.

This authority reflects the Founding Fathers' intention to ensure that military action could be taken judiciously and promptly in times of crisis, allowing for quick decision-making in defense of the nation. While Congress holds the power to declare war, the President's role as Commander-in-Chief allows for significant operational control over the military, including the ability to engage forces in conflict or respond to emergencies that require immediate action.

The other options do not grant the same level of military authority. The Chief Justice of the Supreme Court, for instance, focuses on the judiciary and does not possess any military command power. The Secretary of Defense is responsible for coordinating national defense policies but operates under the authority of the President. Being a member of Congress provides legislative authority but does not confer direct power over military command or operations.