Several weeks ago, before the year's last bell had rung, I found myself in front of a group of very bright students at North Cobb High School.

I sidled up to my topic carefully, beginning with George Washington and the virtue of restraint.

Of all the Founding Fathers, Washington is most famous for what he might have done, but didn’t. After the Battle of Yorktown, he didn’t declare himself King of America. If that sounds strange, it’s because Washington made it so.

After two terms as president, Washington declared his time on stage to be over and walked away. He invented the peaceful hand-off, and so invented the United States.

There was grace on the other side as well. John Adams, who took Washington’s place, did not lock up his predecessor. He did not put Washington in chains or send him to the guillotine, as the French were doing across the pond. That inaction, too, defined us.

I was slow to my point, but eventually got there: We are currently engaged in a hand-off that will dwarf the one faced by Washington, I told the North Cobb students — one that may require more of that virtue of restraint than any founding father imagined.

For the first time in U.S. history, white Americans are about to lose their cherished position as the nation’s majority ethnic group. In 1965, when I was 10 years old, 84 percent of Americans were white. Declining birth rates and decades of changing immigration trends have changed that. The Pew Foundation predicts that whites will cease to be a majority in 2055. The U.S. Census Bureau says it will happen sooner, by 2044.

On a certain level, I felt rather silly delivering this bit of news to this particular group of 18-year-olds. It was like telling Kentucky that there is coal underfoot. North Cobb has 2,790 students: 17 percent Hispanic, 37 percent black, and 36 percent white. The rest of us are in the process of becoming. These kids are already there.

Even so, how this hand-off happens will be the theme of your lives, I told the students. President Donald Trump is only one aspect. The issue lurks in the debate over firearms and gun violence. And in our attitudes toward immigration, obviously.

But truthfully, I lacked the hard data -- a situation that has now been addressed. "The Great Alignment: Race, Party Transformation and the Rise of Donald Trump," by Emory University's Alan Abramowitz, hits the bookshelves this week. (Yale University Press, $35.) My early copy arrived in the mail.

This demographic shift that’s underway has produced something unique to U.S. history, the political scientist writes. “Perhaps the most important and potentially dangerous long-term consequence of the great alignment has been the increasing centrality of issues of race and ethnicity in American politics,” Abramowitz declares. “No other development … has had a greater impact on the rise of political polarization over the past thirty years.”

Most recently, Abramowitz has made waves by identifying what has changed in our approach to politics. He calls it “negative partisanship.” I haven’t given up on finding a better name.

We no longer define our political choices by what we love, but by what we hate, Abramowitz has found. Policy and, in many cases, self-interest, fall by the wayside.

In the chapter that breaks the newest ground, Abramowitz argues that early analyses of Donald Trump’s victory in the 2016 presidential race have it wrong. Economic despair in the Rust Belt and elsewhere doesn’t explain the root strength of Trump’s appeal. Instead, massive amounts of data point to white racial resentment — angst over the current demographic shift — as the reason that Republicans have rallied around and remain attached to Trump, the Emory political scientist writes.

Among Republicans, the election of President Obama enhanced the trend, but it was already there, Abramowitz writes. Traces of the tension can even be found among white voters in the 2008 Democratic primary contest between Obama and Hillary Clinton. It is no coincidence, he notes, that “between 1992 and 2012, the nonwhite share of voters in presidential elections more than doubled, going from 13 to 28 percent.”

I rang up Abramowitz after reading this chapter. This demographic shift can’t be argued with, he said. “In 25 years, the U.S. is going to be a majority minority country. And 10 years after that, the electorate will be majority minority. It’s a gradual thing, but it’s kind of inexorable. Even without much immigration, that trend is going to continue. It’s being driven by people who are already here.”

The shift will happen even faster in Georgia, Abramowitz said. Birth rate trends in the South are being augmented by the return migration of African-Americans. But he’s not ready to say how that will play out in this year’s race for governor, or the 2020 presidential contest.

In the face of irresistible change, the only question is how to adapt. Which brings me back to those students at North Cobb High School.

Demographic succession is far more complicated than one U.S. president handing off power to another, I told these kids. But there is at least one similarity.

In order to work, each one requires grace, forgiveness, and trust. When the time comes to hand over the baton to others, do you refuse to make the exchange? It has happened before. This is what the Jim Crow era of the South was all about.

And once the hand-off occurs, I asked these kids, does the fresh runner turn on the old one, demanding a tit-for-tat settling of scores? I was thinking of Robert Mugabe after he ended white rule in Rhodesia, now called Zimbabwe.

But that was too far afield, so I presented the North Cobb students a situation closer to home: In Georgia, a Democratic party dominated by African-Americans will come to power. Maybe this year, maybe not. But it will happen eventually.

And when it does, what do you do with the Confederate carving on Stone Mountain, the largest, most painfully anachronistic work of art in the South?

We currently have a Democratic nominee for governor, Stacey Abrams, who says she’d remove the carving. We also have the Democratic leader of DeKalb County, CEO Michael Thurmond, who says that Stone Mountain is the very place that the ground rules for the coming demographic hand-off should be negotiated. Republicans, for the most part, have remained silent.

If you’re a student at North Cobb or elsewhere, keep an eye on this. It may tell you something about the world you’re about to inherit.