1. The first president not to complete a term was also the elected president who served for the least number of days in office, completing only 31 days as president. Who was he?
From Quiz DNF - Presidents Who Did Not Finish Their Term
Answer:
William Henry Harrison
William Henry Harrison died on April 4th 1841, his 32nd day in office, of typhoid, pneumonia or paratyphoid fever.
David Rice Atchison was president pro tempore of the Senate for one day, Sunday March 4, 1849, because the incoming president, Zachary Taylor, was not sworn-in until the Monday. He is sometimes said to have been "President for a day", although constitutionally this is not the case.
Franklin Pierce, despite a widely held view of his failures in office, completed his term, and Zachary Taylor held the office for over a year.