In choosing a running mate, presidential candidates often look for someone who?

Presidential candidates often look for someone who possesses the characteristics of balance the ticket. Balancing the ticket means that gaining profit over it to win. In the United States the term balancing the ticket is used in the political term.

When a political candidate selects a running mate from a same party to widespread the campaign then it can be defined as the balancing ticket. There are other meanings of balancing ticket as well.

Someone from a different region can be select as the running mate to provide geographical balance to the ticket. The main purpose of choosing a running mate is to offer ideological, age demo-graphical balance.

they are best described as reliable search engines.