Humphrey in 1968 and Al Gore in 2000. Additionally, former vice president Walter Mondale lost in 1984. In total, 15 vice presidents have become president. Acting president Sections 3 and 4 of the Twenty-fifth Amendment provide for situations where the president is temporarily unable to lead, such as if the president has a surgical procedure, becomes seriously ill or injured, or is otherwise unable to discharge the powers or duties of the presidency. Section3 deals with self-declared incapacity, and Section4 addresses incapacity declared by the joint action of the vice president and of a majority of the Cabinet. While Section4 has never been invoked, Section3 has been invoked on four occasions by three presidents, first in 1985. When invoked on November 19, 2021, Kamala Harris became the first woman in U.S. history to have presidential powers and duties. Sections 3 and 4 were added because there was ambiguity in the ArticleII succession clause regarding a disabled president, including what constituted an "inability", who determined the existence of an inability, and if a vice president became president for the rest of the presidential term in the case of an inability or became merely "acting president". During the 19th and first half of the 20th century several presidents experienced periods of severe illness, physical disability or injury, some lasting for weeks or months. During these times, even though the nation needed effective presidential leadership, no vice president wanted to seem like a usurper, and so power was never transferred. After President Dwight D. Eisenhower openly addressed his health issues and made it a point to enter into an agreement with Vice President Richard Nixon that provided for Nixon to act on his behalf if Eisenhower became unable to provide effective presidential leadership (Nixon did informally assume some of the president's duties for several weeks on each of three occasions when Eisenhower was ill), discussions began in Congress about clearing up the Constitution's ambiguity on the subject. Modern roles The present-day power of the office flows primarily from formal and informal delegations of authority from the president and Congress. These delegations can vary in significance; for example, the vice president is a statutory member of both the National Security Council and the Board of Regents of the Smithsonian Institution. The extent of the roles and functions of the vice president depend on the specific relationship between the president and the vice president, but