I am an originalist in every sense. I want all non-Europeans to be deported to their lands of ancestry (with the exception of natives, who I would be fine with if they stayed here, as Americans allowed in the 1800s, though they did not particularly like them. I'm on the edge with blacks. They are detrimental to American and European society, but the Europeans brought blacks with them to America). I want only men to vote. I want there to be a de facto (not de jure) state religion of Christianity (since America had so many protestant denominations comprising it in its beginning, I will not set a denomination). I want many of the modern-day amendments to be reversed (so basically anything after the Civil War, but that would be quite damaging, so I may change my view to everything being alright provided it was passed before the end of Teddy Roosevelt's second term in office, and keeping the amendment prohibiting people from holding the presidential office more than twice since people no longer respect the founding fathers and must be bound by law instead of their own consciences). But the point is, every moment of our country's prosperity was when it was effectively a white ethnostate, though unofficially. Once we started letting in an abundance of nonwhites and afforded them even the smallest amount of political power, our country started going down the toilet.

So yes, an American constitutional republic would work perfectly in a white ethnostate. Since the American republic has become more corrupt and worsened with the amount of non-European whites in the country, surely having European whites alone would begin to solve problems.