Plot summary
It becomes clear to multiple presidential advisors that Conrad is behaving erratically and out of character. After Conrad insists on destroying five Russian satellites with missiles against the unanimous advice of the National Security Council, Russell and Elizabeth secretly convene the cabinet and vice president. The decision is made to invoke Section 4 of the twenty-fifth amendment. Russell, Elizabeth, and the president's wife confront Conrad with the decision. They offer to let him declare an inability to fulfill his office under Section 3 instead, if he will agree to a medical exam. The medical exam identifies a meningioma intruding on his frontal lobe as the cause of the changes in his behavior. Theresa Hurst steps in as acting president while Conrad is treated.
Credits
Adapted from Wikipedia contributors, Madam Secretary season 4. HTML formatting and reference markers removed.