I'm passionately in support of Bernie Sanders and strongly oppose a Hilary Clinton nomination but it appears that both the party and the media are pushing Clinton. I'm fuzzy on how the nominee is actually selected. Is it by popular vote among the delegates? By popular vote within the caucus(es)? Does Weisserman-Schulz dictate her choice to the delegates? I'm interested in both the "supposed to happen" and the "this is how it actually happens" side of things. Note that what I hope to do is harness this information to best "lobby" (with my voice and piddly financial resources) to see that Bernie Sanders wins the candidacy. Thanks!
The nominee is selected by a vote at Democratic Party's nominating convention.
The voters are elected delegates (pledged to varying degree to follow the results of their states' primaries or caucuses, depending on individual states' rules. There are 3 kinds of binding/pledging covered in Wikipedia); as well as unpledged so-called "Superdelegates", who can vote for whoever they want.
Nominally, Superdelegate's job is to ensure that a radical, unelectable-in-general-election candidate with broad partisan support would be rejected even if they win primaries/caucuses. Wikipedia goes into broad detail over the history.
Who controls superdelegates? It's politics as usual. Some are influenced by more important party bigwigs. Some are influenced by other alliances/allegiances/interests/favors owed. Some have strong opinions and vote who they want.
Most of them are entrenched mainstream politicians and therefore in this case (sad for Sanders and you) don't like emergent "outside" candidacies (OK, it sounds idiotic to call a forever-senator Sanders "outside" but whatevz), both because their less mainstream views are a harder sell in general election; and because establishment never likes insurgents, even - or especially - on their own side.