Seth Masket: “Donald Trump picked Mike Pence as his running mate in 2016 for pretty sound strategic reasons — he wanted to lock down the evangelical Christian wing of the party, which was not yet staunchly in his corner. Today, there is likely no major faction in the party Trump is worrying about winning over, so it’s less clear just whom he might want.”
“There are many different values a party can use as a guideline for picking a VP. Where the candidate is from, how old they are, whether they’ve been running for president, etc., weigh heavily on the choice. But picks usually fall into one of two major categories: ticket-balancing (that is, picking someone from a different faction of the party, ideological position, or geographic region) and reinforcement (that is, picking someone who is in many ways similar to the presidential nominee and would carry on with their agenda). John Kennedy and Lyndon Johnson would be a great example of ticket-balancing, while Bill Clinton and Al Gore are a common example of reinforcement.”