Only in recent history has a more open system of primaries and caucuses been grafted onto the process to give the average American a say in who appears on the general election ballot.
In a close, contentious primary season, however, the veneer of accountability can rub off, exposing the sometimes unsightly gears that still power the US political system.
This has prompted objection from the supporters of two candidates in particular - Donald Trump and Bernie Sanders - who feel that the party establishments are arrayed against their presidential quests.
But are their concerns valid? Read on by clicking on the link below.
Read more: Is the US presidential race 'rigged'? - BBC News