The to the u. s. constitution states that when the president believes that he or she is incapable of performing the duties of the office, he or she must inform congress in writing of this fact.

This information is included in the 25th Amendment to the United States Constitution. This amendment explains what will happen should the President die, resign, or be removed from office, and also allowed for the President to, with his written consent, temporarily pass all of his responsibilities to the Vice President for a period of time without completely resigning from office.