Picking the vice president
Let’s just say off the top that, unlike in the old days, the modern nominating convention has no role in picking the party’s presidential candidate. That function is now in the hands of the person who has locked up the nomination before the convention even starts, and the much-anticipated selection is usually announced days before the convention. Barack Obama announced Joe Biden, and John McCain announced Sarah Palin, as their running mates two days before their respective conventions in 2008. Hillary Clinton and Donald Trump announced their VP picks—Tim Kaine and Mike Pence—three days before the start of their conventions in 2016. Even at the 1980 Republican convention, Ronald Reagan announced his choice of former rival George H.W. Bush on the penultimate day of the gathering. The delegates themselves had no official role in making these choices.
But it wasn’t always this way.
In the first four presidential elections, the man who gained the second highest number of electoral votes became the vice president. That George Washington would be president twice was never in doubt, but in 1796, John Adams’ then-political archrival Thomas Jefferson became vice president; and in 1800 nominal party allies Jefferson and Aaron Burr tied for the most votes, throwing the selection to the House, in which Jefferson prevailed. Burr became vice president, and was thereafter marginalized. This made for some pretty unhappy presidential/vice presidential pairs.
The Twelfth Amendment, ratified in 1804, fixed this by requiring separate electoral votes for each office, and has governed election of the vice president from that year to the present.
Starting with the Republican National Convention in 1831, the vice president was on the agenda, but the choice was not in the hands of the presidential nominee. Party elites would negotiate with the nominee over who would get the VP nod, taking into consideration issues like regional and ideological "balance." Those were the days of the "brokered" convention.
In 1900, for example, New York Republican bosses pushed a reluctant Governor Theodore Roosevelt on to the McKinley ticket, partly in an effort to get Roosevelt and his reform program out of Albany. And again in 1904, the GOP Convention forced Indiana Senator Charles Fairbanks onto the ticket with President Roosevelt in an attempt by the party’s "old guard" to temper Roosevelt’s reformist energy. In a deal brokered at the 1932 Democratic convention, House Speaker John Nance Garner became Franklin Roosevelt’s running mate.
But this "arranged marriage" style of assembling the ticket, as Elaine Kamarck explains in her report on the modern vice presidency, began to change in 1976 when Minnesota Senator Walter Mondale went through a formal vetting process to become Jimmy Carter’s running mate. Carter, not the party elites at the convention, chose Mondale. There was no deal with party elites to install Mondale on the ticket. However, Carter’s choice was still rooted in regional and ideological balance, like in the brokered conventions in the past.
This change also began to herald a transformation in the prestige and power of the vice president. Until the late 20th century, the vice president of the United States occupied an ill-defined role and was often left out of Oval Office policy decisions. The arranged marriage between two men who were often ideological rivals (though of the same party) meant that after the election the president just didn’t pay much attention to the vice president, whose only job seemed to be his availability to assume the higher office in the worst case scenario (and eight of them did after the president died in office). Carter’s selection of Mondale in 1976 changed the way the vice president was added to the ticket, and Bill Clinton’s selection of Al Gore as his running mate in 1992 rebuffed the balance approach that had prevailed until then. As Kamarck put it, "there wasn’t even a whiff of balance about the Clinton/Gore ticket." Both were young, southern, and from the more conservative wing of the Democratic Party. This ushered in, as Kamarck explained, the "partnership" model of the president-vice president ticket.