Vice presidential candidate Tim Kaine will address the Democratic National Convention Wednesday in Philadelphia. Kaine and Republican VP selection Mike Pence emerged as the nominees after weeks of intense public speculation. Here, Bill Crotty, professor emeritus and an expert on presidential politics, examines how presidential hopefuls select their running mates and whether those selections typically impact elections.

What impact do vice presidential selections typically have on an election?

Vice presidential selection can be something of an open-ended mess, creating as many problems for a candidate as it can help with an election. The actual impact of a vice presidential nomination on an election varies greatly. Most have little direct consequence. The presidential nominee carries the ticket and makes the argument for his or her election. This of course is the crucial choice. The VP nominee complements whatever weaknesses in style, ideology, or political or geographical balance—or in buying off a party faction—the candidate thinks necessary. I believe most presidential candidates hope for some plus from their choice but mostly do not want anyone who hurts the ticket or will upstage the nominee. It can be an arbitrary and personal decision and, in fact, is a rather awkward appendage to the whole process and something of an eventual backdoor to the president’s office.

What are some of the strategies employed in selecting a vice presidential candidate, such as geographical or ideological considerations to win a swing state or balance the ticket?

Assuming an optimum outcome, the vice presidential selection is intended to be an electoral plus, adding balance to the ticket and hopefully greater voter appeal. Also, the folk wisdom is that these nominees should be able to take on the responsibilities of the presidency in a heartbeat. The political considerations are far more important than any presidential potential. As for balance, that depends on the candidate’s perceived weak points. It can be geographical, ideological, a buy-off of a party faction, a cover for a weak or unpopular campaigner, or simply someone the candidate likes and can get along with.

It is fascinating reviewing the choices presidential nominees have made and the reasoning behind them. John Kennedy’s choice of Lyndon Johnson after a bitter nomination contest was unpopular with Robert Kennedy and northern liberals. Johnson added a regional and believed ideological balance—though he turned out to be far more liberal than Kennedy—and no one questioned his experience or ability to handle the president’s office. Jimmy Carter chose Walter Mondale for ideological balance and a broader party-based appeal. Mondale was adventuresome and went for gender balance, picking Geraldine Ferraro, a risky decision given her husband’s associates and business dealings. An apolitical and older Dwight Eisenhower was forced to take Richard Nixon, a man he neither liked nor respected, to give conservative party credentials to his candidacy and a younger, considerably more aggressive campaigner to carry the party’s message.

One of the more exciting but disastrous choices was John McCain’s selection of the unknown governor of Alaska, Sarah Palin, as his running mate. It is a long story and a prime example of how not to vet a prospective nominee, but Palin, while outgoing, likeable, and personable, knew nothing of policy issues or much of government outside of Alaska. The level of her ignorance was startling. It is unlikely McCain or any Republican could have won under any circumstances given the Great Recession, but the choice of Palin made a mockery of the process and the idea of someone a heartbeat away from the presidency.

Donald Trump selected Mike Pence, a governor from the nation’s heartland who describes himself as “a Christian, a conservative, and a Republican. In that order.” Hillary Clinton selected Tim Kaine, a centrist senator from a swing state. What were the candidates looking to achieve with their running mate selections?

Donald Trump decided on Mike Pence, likely not to add any geographical balance to his run but to signal a move toward Republican orthodoxy and, hopefully for Republicans, add a sense of stability and predictability to his campaign. It is not likely to happen.

Pence is a solid, committed economic and social conservative with an unquestioned belief in Republican small government, a deregulated economy, minimal tax approach, and a corporatized if solidly Evangelical-based religious state. He is clearly a concession to the Republican Party’s conservative core. I expect, given Trump’s unpredictability, ad hoc issue views, and personal attacks, Republicans breathed a sigh of relief.

Hillary Clinton’s choice of Virginia Sen. Tim Kaine is more conventional. Kaine has been considered before and is a well-liked centrist with a pleasing personality, few enemies, and moderate Southern credentials. He also is fluent in Spanish, which should help with Latino voters. He is a safe choice and a comfortable one that solidifies the ticket, though there are risks involved in the choice with a party more divided than it may seem.

It should be quite an election. Both parties have positioned themselves well for the fight to come.