Three different paths can lead to the vice president becoming president through succession. first, when a president dies in office, the vice president becomes president. eight of the nine vice presidents who have become president through succession did so for this reason. second, if the president is unable to perform his or her duties, the vice president takes up the role. this might happen if a president becomes physically sick or mentally unstable. third, if a president resigns or is impeached, again, the vice president takes the office. this has happened once in us history. a few of the vice presidents who became president in these ways were later elected president. the first was theodore roosevelt in 1901. many twentieth-century vice presidents have used the same desk that he used. in rare cases, the vice president may not be able to serve as president. when that occurs, the next person in line is the speaker of the house of representatives. if he or she cannot serve, the president pro tempore of the senate becomes president.