The President who is unable to exercise the powers and duties of the office remains the President of the United States during the period when there is an acting president; in other words, the incapacitated President does not become an ordinary citizen.
The President remains the President of the United States during the period when there is an acting president. This President is unable to exercise the powers and duties of the office. The incapacitated President does not become an ordinary citizen. This is in other words.