The roles of the vice-presidential candidate are to support the platform established by the presidential candidate as well as to convince voters that he is competent to be second-in-command of the executive branch. The role of vice president is the second most powerful in the nation.
Although the vice president often exists in the shadow of the president, the role of vice-president is a very important one. If, for any reason, the president cannot fulfill his term, the vice president steps into the role of president. Since presidential candidates choose their running mates, the selection of vice-presidential candidates is often very telling about a presidential candidate's goals. Vice-presidential candidates' skills and experience are typically complementary to those issues presidential candidates deem of highest priority.
Since a vice-presidential candidate technically presides over the Senate and could also prospectively be president, he is expected to present himself in a way that promotes a sense of cohesive leadership as well effective communication amongst the members of the respective party ticket. Although the vice-presidential candidate now runs on a ticket with the presidential candidate during elections, this was not the case prior to 1804. Until then, the presidential candidate who received the most votes became the president, and the candidate with the second most votes became the vice-president.