If the vice president dies in office or resigns, the president chooses a successor under the 25th Amendment. The president's selection is subject to confirmation by majority votes of the House of Representatives and the Senate.
The 25th Amendment was ratified in 1967. The need for this amendment was highlighted by President Kennedy's assassination. His successor, President Lyndon B. Johnson, served 14 months with no vice president, since there was no constitutional process for replacing a vice president. In 1973, President Nixon used the amendment to replace Vice President Agnew, who resigned. In 1974, President Ford used it to appoint a vice president. The office was vacated when Vice President Ford became president after President Nixon's resignation. .