Section 3 allows for the prez by written declaration to the President Pro Tempore of the Senate and the Speaker of the House state to state that he is unfit to hold the office. Section 4 gives that weapon to the veep and cabinet members/Congress. Mental incapacitation. The Constitution does not require mental health professionals to test/interview/evaluate/conclude. It only requires the veep and specific others to conclude that the prez is unfit to discharge the powers and duties of his office. After written declaration to the President Prop Tempore of the Senate and the Speaker of the House it allows for the veep to immediately assume the powers and duties of an Acting President. They can do that on the high seas to a captain. It's called mutiny. So are we in for mutinous times ahead?