In the United States, after all the long drawn out process of choosing the presidential nominee of a major party, is the selection of the vice presidential nominee the private decision of one person? Does the presidential nominee (I'm thinking specifically of Joe Biden in this year's election) have the sole power to select his running mate, and have his choice rubber-stamped by the party convention? Or is the selection of a running mate the subject of backroom negotiations between the presidential nominee and other party leaders?
Nowadays, the candidate and his campaign have the real power here, although obviously he consults with advisors and is subject to all kinds of influence. Here is a recent piece in the Washington Post which compares Biden's process with Carter's in 1976.
Carter and his staff established a modern vice-presidential selection process, designed to replace the chaotic behind-the-scenes maneuvering in smoke-filled rooms at the convention with a fresh, relatively transparent interview and vetting process that simultaneously fueled a dramatic media narrative in the days leading up to the convention.
Even though Carter publicly vetted his running mates for the benefit of front-line journalists, he carefully guarded his selection until the campaign’s self-orchestrated big reveal at the convention. Subsequently, amid dissatisfaction about the dramatic shift in tradition, the vice-presidential selection process became much more opaque and secretive in coming years as candidates tried to build suspense until the appropriate time at the convention.