I stand corrected. The density of the African-American population varies from state to state, though, and PR makes it possible not to be beholden to the (former) Democrats any longer. I don't know if a significant portion join the Religious Republican party or stay with the Social Democrats. I'm sure that a scant few members of the AANC will make it through, especially in Florida and Georgia.
If anything, the adoption of PR would make blacks more powerful, especially if they hold out on passing legislation needed for government, whether as members of the mainstream or the AANC.
Indeed. In NZ we currently have a Maori Party that formed out of the Labour Party 6 or 7 years back after a specific and highly controversial disagreement over coastal foreshore ownership policy. This new party is pretty influential at present as it is in support of the right wing Coalition government. Despite the party itself being primarily made up of former Labour activists and its voter base still largely voting Labour for the Party Vote (as opposed to the Maori Party for the Electorate Vote).