On October 10, 1973, the vice presidency had become vacant for the second time because of a resignation. It had been vacant because of death 7 times, the last being James Sherman in 1912. While Richard Nixon's resignation from the presidency the following year would be a first for that office, it would not be for his second-in-command. When Nixon chose a running-mate in 1968, he chose a little known governor, Spiro Agnew, instead of a star that would take attention away from the top of the ticket. What Agnew did bring was that attack dog persona and while a moderate in the GOP appeased conservatives and southerns, since he was from Maryland. Nixon hoped Agnew would resign before the 1972 reelection so he'd be easier to replace with Nixon's preferred vice president, John Connally, the guy that also got shot, but only wounded, on November 22, 1963.
Agnew was reelected VPOTUS with Nixon in 1972, Nixon had deal with his decision from 1968 for another four years, or would he? When Baltimore started cleaning up corruption, investigations led to corruption in the Governor's Office, the former governor turned vice president of the United States. Nixon eventually got his wish, but he got it too late. Agnew resigned in the first year of the second term, 1973, and became the first vice president to resign because he faced criminal charges, among them bribery and tax evasion.
With Agnew's resignation, there was a vacancy in the vice presidency for the first time since the States ratified the 25th Amendment in 1967, just 6 years earlier. Nixon became the first president to appoint a vice president, not including nominating conventions, but because the Constitution says so. However, by the end of 1973, Nixon was not as popular as he was just a year prior when he won one of the biggest landslides in presidential history. Watergate continued to grow from a piece in the Washington Post in June of 1972, to investigation of the president and threat of impeachment if he does not comply. Nixon had to choose someone that was not going to divide the country any more than his administration had achieved by covering up the Watergate scandal and no cooperating with the Congress. Connally, a Democrat turned Republican, would not be a favorite for Republicans in Congress, both the House and the Senate, for fear of Nixon's removal would put a scalawag in office. Nixon was in no position to get what he wanted.
Less than 2 months after Agnew's resignation, Gerald Ford became the first appointed vice president after both houses of Congress confirmed him on December 6, 1973, the Senate confirmed him over a week before the House. The new vice president, "a Ford, not a Lincoln", easily won the votes because he was a moderate and a nice guy. He served in the House of Representatives for 24 years and only sought to be the Speaker of the House of Representatives, one-half of the leadership of the Legislative Branch of the United States, the Congress. Instead he'd have to settle for the other half, the vice presidency, which is also, the President of the Senate. The 40th VPOTUS would go on to be the 38th POTUS after the 37th resigns in August of the next year. Connally and Agnew, almost became president, but politics, and the law, came into play as it always does.
The ticket of Nixon/Agnew won the 1968 election in one of the closest elections and won reelection in a landslide only Roosevelt 32 and Johnson 36 had accomplished. The ticket of Nixon/Agnew would not last the full second term, and become the only ticket to resign before the term expired...so far, of course. (2013) History showed that John C. Calhoun's resignation was not a one-time occurrence, just a rarity.
Calhoun, resigned for different reasons. Calhoun and Agnew share nothing more than being known for their resignations. While Agnew had a short rise from Baltimore County Executive to the Vice presidency in just six years, Calhoun is an American political legend. They both were southerners, but Calhoun was from South Carolina and not a border State like Maryland. They didn't get along that great with their Chief Executive. While Nixon tried his best to avoid Agnew and realized, when it was too late to replace him, that Agnew was not smart enough for the job of Commander-in-Chief (so avoiding him, is a great way to prep him for the job). Calhoun did not get along with his President either, Andrew Jackson. And Jackson wasn't even Calhoun's first President. He was the second VPOTUS to serve two presidents. Calhoun won election to the vice presidency in 1824, when he was on both John Quincy Adams' ticket and Jackson's ticket. In that uncertain election, the House of Representatives chose Adams to be the president while Calhoun easily won enough Electoral Votes to win the vice presidency. He won reelection to the office when Jackson ran again in 1828, but wouldn't be around by election day in 1832.
Calhoun was proponent of States' Rights and limiting the power of the Federal government, which rankled Jackson. The president even threatened to go to South Carolina and hang Calhoun. Calhoun would eventually resign to win a seat in the Senate where he could do more against Jackson than as his Vice President, a weak and powerless office at the time. Martin Van Buren would be put on the bottom of the ticket in '32 and win election with Jackson. Van Buren would then gain Jackson's approval as his heir-apparent in the 1836 election. Van Buren easily won.
Unlike Agnew, Calhoun would continue his illustrious career defending the peculiar institution of slavery, illustrious to southerners, not those in favor of progress like the Abolitionists, while serving in some capacity in the Federal Government of the United States. Agnew would go into political obscurity and really only reappear at Nixon's funeral in 1994, three years before his own death. Because of Nixon's resignation in 1974, Ford's elevation to the presidency created another vacancy in the vice presidency. Ford appointed Nelson Rockefeller to his recently vacated office. The Ford/Rockefeller Administration became the first where neither the president or vice president had campaigned for the offices. From then on, there would be no vacancies in the vice presidency...so far.