Joe Biden is rumored to decide soon on who his "running mate" will be. It's arguably the most important decision Biden will reach as a presidential candidate. Whatever a presidential candidate in the USA says or promises during the election campaign can be changed after the election. Even the party platform that is adopted at the party convention is actually not binding for the candidate. But there is one exception: the choice of the vice presidential candidate.

If Joe Biden gets elected as president of the USA on November 3, that person will then become the next vice president. The constitution says that if a president dies in office or is removed from it, then the vice president takes automatically over. In that sense, it is often said that the vice president is a heartbeat away from the presidency. In the case of Biden, we're talking about a 77-year-old heart. Since Biden would probably not run again in four years, his or her vice president would then become the de facto front runner for the Democratic nomination in 2024. All of that makes this the most important vice presidential pick in a long time.

Political scientists have filled libraries with studies about the impact of the vice presidential candidate on the campaign. Most of the time, it's minimal. The conensus is that a vice presidential candidate can boost the ticket in his or her own home state by a couple of percentage points. Historically, geography therefore played an important role in the choice. This time around, however, gender and race will probably be much more important factors.