With increased demographic change and ever diverging interests of the races in America, I believe the best solution to avoid conflict is for the major racial groups (White, Black, and Hispanic) to have their own ethnostates to represent their people and respective interests. These ethnostates wouldn't necessarily have to be their own sovereign nations, but rather inspired by both the Russian and Swiss systems (the latter especially), would be autonomous regions within the same nation.
The federal government would have control over matters of defense, diplomacy and trade, while these ethnostates would have control over their own form of taxation, immigration, education and social programs, etc. as seen fit by the respective people of each of these ethnostates. (Similar in a way to the Swiss canton system)
This would not only be desirable, but also possible and very practical with the current demographic concentrations.
My proposal would separate this new "American Federation" in 3 to 4 ethnostates.
These ethnostates also have the advantage of being near zones of cultural and racial similarity, the Hispanic homeland being next to the rest of latin america, the Black homeland being close to the afro carribean community, and the White homeland being next to Canada.
Let me know what you think of this idea and if you notice any flaws or would like to add something.