The majority of younger Americans are already non-white

The change has broad implications for identity and for the country’s political and economic life, transforming a mostly white baby boomer society into a multiethnic and racial patchwork. A majority of the youngest Americans are already nonwhite and look less like older generations than at any point in modern American history. In California, 52 percent of all children are living in homes with at least one immigrant parent, Professor Sáenz said.

end partial quote from:

Fewer Births Than Deaths Among Whites in Majority of U.S. States

But, maybe you aren't understanding this because what they mean by non-white is not just black but also hispanic and middle eastern and asian and even native Americans from North, South and Central America. So, if you are thinking black (no they are way outnumbered by other groups.

Blacks are ONLY 12.3% of the population. Most of the change is actually native American and hispanic from North, South and Central America now. But, also richer Chinese are buying their way into the U.S. because of laws enacted during the Great Recession to help the financial recovery of the nation.

However, unless you were in the stock market before, during or after the Great Recession mostly people who were middle class, and poor were screwed completely by the Great Recession and that hasn't really changed except they mostly all have jobs now instead of losing their homes while going bankrupt like they did during the Great Recession (whose causes were actually much much worse than the Great Depression). We really lucked out having people like  Bernanke at the Fed and Geitner at the treasury or else billions would have died worldwide by now from starvation from the 2nd Great Depression worldwide.

So, I would say the biggest reason Whites are presently going extinct slowly in the U.S. is the Great Recession and the damage they never recovered from and Trump's slogan which is in reality: 

"Only the  white rich should survive Anyway!"

Which was not his slogan during the campaign.

So, once again the white Republican rank and file have been betrayed by their leaders.

And it looks like they are slowly going extinct because of it. (at least here in the U.S.)