I must have missed the announcement that “middle America” was all white now. I’ll alert the Times.
Tony Santos

Middle America (which I consider to comprise middle income people who live in the interior of the United States) tend to be more white than the coasts or urban centers, in terms of racial diversity.

Here’s data from Pew:

As the nation has become more racially and ethnically diverse in recent decades, so have middle-income adults. Whites are now about two-thirds of middle-income adults (67%), a decline from their 80% representation in 1971. This trend parallels the pattern for all adults, as does the increase in Hispanics and blacks as a share of middle-income adults. Hispanics, 15% of middle-income adults in 2015, were 11% of this group in 1971. Blacks, 11% of middle-income adults in 2015, were 7% in 1971. The share of Asians among middle-income adults, 6% in 2015, has doubled since 1991, the earliest year that data are available for this racial group.
Middle-income adults in 2015 were more likely to be white (67%) than lower-income adults (52%) but less likely than upper-income adults (77%). Middle-income adults in 2015 were less likely to be black or Hispanic than lower-income adults, but more likely than upper-income adults.

NPR has an additional perspective.