Every four years, presidential candidates select their running mates. These announcements are one of the dominant news events of the election cycle, generating endless speculation about how the running mates will affect the campaign. All of this is typically predicated on the assumption that vice presidential candidates must shape the race in some way. Christopher J. Devine and Kyle C. Kopko engage that assumption, giving us perhaps the best source to date that explores how, when, and why running mates matter. Their answer: vice presidential candidates can affect elections, but their effects are probably small and the story is more complex than is often assumed.

In Do Running Mates Matter?, Devine and Kopko establish that presidential candidates dutifully cite the “VP Formula,” consistently saying that their most important consideration is picking a candidate who can help them govern and/or assume the presidency if necessary. Yet presidential candidates also seem to believe that a “game changer” can help them close the gap if they are behind, which suggests that they believe the right running mate can swing votes. Voters appear to share this belief; as Devine and Kopko demonstrate, about 80 percent of voters cited the vice presidential candidate as contributing to their vote choice in