Once a sufficient critical mass of citizens is achieved (you've see the same reports as I of massive inter-state migration), then the history of manifest destiny will merely be replayed as territory is reconquered.
No one ever learns from history - it simply isn't in our DNA. We must repeat the same steps & processes of our fore-fathers over & over again to achieve the same damn result.
The nation will be lost as we lose our national identity and shared sense of endeavor. The impact of unbridled and less diverse immigration will be to change the entire country, not just the western states. We will take on the profile of a third world country with a large, permanent underclass and a wealthy elite living in walled compounds with private guards. This country will be taken down thru its own democratic institutions, i.e., thru the ballot box.