[Julian E. Zelizer is a professor of history and public affairs at Princeton University. He is the co-editor of “Rightward Bound: Making America Conservative in the 1970s” (Harvard University Press) and is completing a book on the history of national security politics since World War II.]

... The running mate selection is more important today than it was in previous decades, because the power of the office has vastly expanded. The transformation of the vice presidency began in the 1950s with Nixon, who served under President Dwight Eisenhower. In the famous Kitchen Debate in 1959, it was Nixon who took on Soviet Premier Nikita Khrushchev about the virtues of capitalism. Under President Jimmy Carter, Vice President Walter Mondale accelerated the trend of vice presidential activism, which has culminated with the current influence of Vice President Cheney, who has helped define administration policy on almost every issue, ranging from environmental policy to the war on terrorism. And when Americans think of the vice presidency, they’ll never be able to erase the image of Cheney. This is no longer an office, as Franklin D. Roosevelt’s first vice president, John Garner, once said, that is “not worth a bucket of piss.”

History offers a road map about how not to choose a running mate. In 1972, Democratic nominee George McGovern’s choice of Missouri Sen. Thomas Eagleton as his running mate turned into a political nightmare. A few weeks after being nominated, Eagleton revealed to reporters that, during the 1960s, he had been hospitalized several times for nervous exhaustion, including electric shock treatment. The revelations came out in an era when Americans saw psychiatric therapy for public officials as a sign of weakness. As McGovern came under pressure from party officials, Eagleton withdrew his nomination. The whole incident turned into a sign that McGovern was not a capable decision maker. Already facing an uphill challenge against Nixon and a deeply divided Democratic Party, he lost 49 states.

Or consider Pennsylvania Sen. Richard Schweiker, insurgent Republican candidate Ronald Reagan’s choice as running mate in his 1976 nomination challenge to President Gerald Ford. Running to the president’s right, Reagan did unexpectedly well in the primaries by painting Ford as a centrist whose foreign policies were undermining America’s position in the Cold War and whose domestic policies had failed to stop stagflation. Reagan tapped into the energy of the conservative movement, which had emerged in the 1970s as a powerful force in national politics.

The primaries were neck and neck. The decision of a nominee was not resolved when the primaries ended. Seeking to make a dramatic choice before the Republican convention in order to win over independent voters, Reagan’s campaign manager, John Sears, convinced him to select Schweiker, who embodied the type of moderate political views that Reagan supporters detested. The plan backfired. Reagan’s choice totally contradicted the image that he had developed and weakened the enthusiasm of conservative activists in the crucial weeks going into the convention. Ford won the nomination by a few more than 100 delegates.

Sometimes presidential candidates have been able to overcome bad choices. In 1988, George H.W. Bush picked Indiana Sen. Dan Quayle as his running mate in his presidential campaign against Massachusetts Gov. Michael Dukakis. The Bush campaign believed that Quayle was a strong candidate because he was closely allied with the right wing of the GOP (which distrusted Bush). In an era of television politics, Quayle was also young and attractive. The contrast with Dukakis’ more senior running mate, Sen. Lloyd Bentsen of Texas, would be dramatic. Quayle promised to offer a new face to conservatism and add some pizzazz to the ticket.

But Quayle turned out to be an embarrassment for Bush — a decision Bush had to overcome rather than one that brought him strength. Quayle looked so young on television that his appearance opened up questions about his experience and capacity to govern. It turned out that his family had helped this Cold War hawk obtain a position in the National Guard during the 1960s. Embarrassing blunders created fears about his intelligence. And Bentsen famously lacerated Quayle in the vice presidential debate, dismissing him as “no Jack Kennedy.”

There are successful choices that might be more instructive for the current candidates. Good running mates bring regional balance to the ticket. Sen. Lyndon Johnson was a brilliant pick for John F. Kennedy in 1960. Despite the animosity that existed between the candidates, Johnson helped Kennedy win the South in an extremely close election, and he gave the Democratic establishment hope that Kennedy would be able to work with Congress. Good running mates can bolster confidence about experience and the ability to work with a broad range of groups. In 1980, Reagan was still seen as a maverick and as a politician who was allied with the conservative movement. Reagan’s decision to run with the elder Bush, a classic establishment figure, helped give voters and Republican leaders confidence about how Reagan would govern....