[Platapus]

1832 until 1940, the VP was picked by the delegates at the convention. It should be remembered that prior to the 1960's, the VP had little to do in the Executive Branch and spent most of their time in the Legislative Branch.

In 1940, FDR threatened to refuse the nomination if the delegates did not nominate Wallace. In 1944, partially to poor health, FDR allowed the delegates to choose the VP -- Truman.

Since 1948, the presidential candidate gets to choose, but I am sure there is behind the scenes influence from the party. Like most things in politics, it is probably a compromise. The presidential candidate wants to select a VP candidate that the party supports. It serves no purpose to buck one's own party too much. Conversely, there is no point to force a presidential candidate to have a running mate he or she dislikes.... Although the relationship between president and VP is not always friendly.

In 1984, Walter Mondale had two significant "firsts"

He was the first candidate from a major party to nominate a woman as VP and he was the first candidate to announce his running make prior to the convention. Prior to that, the announcement of the VP candidate was made near the middle of the convention.