Had the Senate race in Arizona earlier this month come down to only white votes, exit polling suggests that Rep. Martha McSally (R) would have won easily. Among whites, she had an eight-point advantage over Rep. Kyrsten Sinema (D-Ariz.). Unfortunately for McSally, though, an estimated one-fifth of the electorate in the state was Hispanic, and among those voters, Sinema had a 40-point advantage.

And so: Senator-elect Kyrsten Sinema.

That’s the quiet (and not-so-quiet) fear of many Republican strategists. An America that is becoming consistently less densely white is an America in which the current iteration of the Republican Party is at a growing disadvantage, given the general preference shown by Hispanic and black Americans to Democratic policies and candidates.

But the problem for the GOP isn’t really about current voters. It’s mostly about future voters. And new data from Pew Research Center shows why that concern is warranted.

Pew broke out the population of Americans ages 6 to 21 by demographic. In 2018, it estimates, about 52 percent of people in that age group were white. By contrast, in 1968, young baby boomers were about 82 percent white.

What 52 percent white means, of course, is that 48 percent of those young people are nonwhite.

We can demonstrate why this is worrisome to the Republican Party in two graphs. The first comes from Pew data released in March, looking at the political identity of those in the millennial generation (a term used by Pew to refer to those born from 1981 to 1996). Among millennials, whites prefer the Democratic to the Republican Party by 11 points. Among nonwhites? The preference is 54 points.

Tufts University political science professor Brian Schaffner used data from the Cooperative Congressional Election Study and his own analysis to show how the share of votes earned by Democrats changed by age from 2010 to 2018. In 2010, most young people preferred Democrats, but that preference quickly dropped off. In 2018, according to his analysis, that preference was steady into a significantly older cohort of voters.

When he warns about the curve “shifting to the right,” he means that the GOP should be concerned that the strong preference for Democratic voters will continue into older and older ages — in part a function of that strong preference for Democrats among nonwhite Americans, who make up more of the younger population.

Earlier this week, we looked at whether demographic shifts were already aiding the Democratic Party. The shifts themselves, we found, didn’t necessarily translate into more success for Democratic candidates in every state. While every state got less white since the early 1990s, the results by party in any individual state were mixed.

Overall, though, in those states with the biggest decreases in the density of the white population, voting in Senate and gubernatorial elections did tend to shift to the left.

Here we’ll share a chart using estimates of the composition of the next Congress based on the results of contests as of Tuesday. It’s not a coincidence, one can assume, that the incoming Democratic caucus is a lot less heavily white than is the Republican one.

Pew’s analysis of the demographic composition of younger people in the United States found that the diversity shift was similarly uneven. In the Midwest, two-thirds of those age 6 to 21 are white. In the West, though, a region that is among the fastest-growing, people in that age group were as likely to be white as Hispanic.

This, in part, is why the region has grown so fast. Fertility rates among Hispanic women, an estimate of the number of children a woman will have over the span of her life, have been higher than rates among other groups (though that figure dropped in the most recent government analysis).

There’s another noteworthy aspect to the growth in the density of the Hispanic population among young residents. In 2002, nearly a quarter of young Hispanics in the United States were born outside the country. Now, more than half are born in the United States to immigrant parents.

There’s an important subtext to that, too: There is a much higher density of young Hispanics now than in 2002 who were born as citizens — and can therefore vote.