Under which authority may the President call up the National Guard?

The National Guard can be called up by the President under Title 32, United States Code. This provision allows the President to mobilize the National Guard as part of state or federal military operations while retaining the Guard's status as a state force. In this capacity, the National Guard can perform functions in support of federal missions, including responding to natural disasters or civil disturbances.

Under Title 32 authority, National Guard members continue to be paid by their state, but they operate under federal authority and oversight. This distinguishes it from Title 10, where the President has the authority to federalize the National Guard, resulting in the members being placed on federal active duty. Title 32 is particularly relevant because it maintains the Guard's connection to state governance while allowing federal support to be provided when necessary.

The other options, while relevant to various aspects of military operations, do not specifically pertain to the President's authority to call up the National Guard in the manner described by the question. Title 10 deals more with the organization and use of the armed forces overall, the National Defense Authorization Act outlines funding and policies for the military, and the Military Commissions Act focuses on the legal framework for military commissions rather than the mobilization of the National Guard.