What do you mean 'those guys'? You know nothing about me.
Democrats have talked about changing demographics and 'the emerging Democratic majority' since the beginning of this century. All of the rhetoric from Obama's elections have been about how the new, multicultural america has made a Democratic consensus irreversible.
Whether or not this was true (as I've said in an earlier post re Hispanic males, theres plenty of evidence it's not), ethno-nationalism is extremely volatile and works both ways. Republican appeals to whites have met limited success before. It took the perception that the Democratic party no longer needed them for working class white people to vote for Trump in historic numbers.
The GOP is now the White Party. The Democrats need to adapt to deal with this, they can't play the same tune louder and expect more people to sing along.
I agree that the GOP has become a white nationalist party and that America is in a battle against white nationalism.
Your suggestion that the solution to this is for the Democrats to avoid putting people of color and Muslims in leadership positions seems...problematic.
The Democrats won the popular vote by a large margin and lost in a few states, which they didn't campaign in effectively, by around 70,000 votes. They did this in the face of the organized security apparatuses of two countries -- America and Russia -- overtly attempting to destroy their candidate.
I think my solution for next time would be to run a candidate that is hated less and try harder in the Rust Belt to connect with the Democratic base, rather than decide that America is just a white nationalist country now and so minorities are going to have to get off the boat.