Wikipedia says that "the first state in the United States to hold its presidential primary was North Dakota in 1912." (https://en.wikipedia.org/wiki/United_States_presidential_primary) So I'm confused. I also had a look at that 1968 Democrat convention and see that the LOOSER of the primaries won the nomination! So that confused me too! American politics is CONFUSING!
There were a few states who had "beauty contest" to help the state party decide who'd they support at the convention, most were non-binding. It was after the HUGE upheaval and fight at the Democrat 1968 convention in Chicago that it went national so that the candidate would be "hopefully" decided before the convention and the convention became a christening ceremony instead of the decider. They have been pretty boring ever since.
Kamala is the veep nominee. She's multi-racial. Obviously, not inviting Gabbard has to do with her refusal to vote for impeachment; it has nothing to do with race.