Which two Presidents were incapacitated for long periods while still in office?

Answer 1

James A Garfield was incapacitated for three months after being shot by Charles Giteau. Her then died and was succeeded by Chester Arthur. This episode led to a change in the Presidential succession law, since there was neither a President of the Senate nor a Speaker of the House at the time, and had Arthur also died during that interval, the US would have had no lawful President. The Presidential Succession Act of 1886 removed those officers from the succession, replacing them with the Cabinet heads, in order of seniority.
Woodrow Wilson was largely (though not totally) incapacitated for 18 months following his stroke in September 1919. He receivd very few visditors during this period, which gave rise to many wild rumours, eg that he had gone insane. Both then and later, there were claims that his wife, Edith Galt Wilson, had been running the country during his illness, something she always denied. Wilson died in 1924, only three years after leaving office. The episode led to concerns about the inadequate legal provision for possible Presidential disability, yet almost nothing was done until the passage of the 25th Amendment in 1965. Because of the legal uncertainties, neither of the Vice-Presidents, Chester A Arthur and Thomas R Marshall, had made any attempt to claim Presidential authority during these "interregnums".