Campaigning for the Democratic presidential nomination in 2004, Senator John Edwards of North Carolina often spoke of “two Americas”: the haves and have-nots. We Republicans hooted at this. Edwards seemed to be saying that half the country was in dire straits. In the middle of the Great Depression, FDR had spoken of only a third! (“Ill-housed, ill-clad, ill-nourished.”)

Edwards lost the nomination to another senator, John Kerry of Massachusetts. But Kerry made him his running mate. At the Republican convention in New York, Rudy Giuliani, the ex-mayor of that city, had a little fun with the Democratic ticket. Kerry liked to take two positions on issues, Giuliani said. “Maybe this explains John Edwards’s need for two Americas.” We laughed our heads off.

Some of us aren’t laughing now. The country is clearly divided, though not between haves and have-nots: There are rich, poor, and in between on either side. The country is divided between “red” and “blue,” “conservative” and “liberal,” Fox and CNN, etc. We are divided not just by culture and politics, but also by geography. Those of like mind tend to live together. Americans are hived off.

In 1980, there were about 400 “landslide counties” — counties in which one presidential candidate walloped the other. Votes from those counties accounted for 4 percent of the total. In 2020, there were about 1,700 landslide counties, whose votes accounted for 35 percent of the total.

After the election last month, a report in the Wall Street Journal put it this way:

If it feels like Republicans and Democrats are living in different worlds, it’s because they are. There are few places left in America where one tribe of voters is likely to encounter the other. Predominantly white, rural areas are solid Republican; urban areas are dominated by Democrats.

Above, I mentioned Fox and CNN. In October, the Pew Research Center asked the question, “Has the United States done all it can to control the coronavirus?” Among those who rely on Fox or talk radio for information, 90 percent said yes. Among those who rely on CNN and similar outlets, 3 percent said yes.

I hardly know a starker stat.

An expert on all this is David French, a writer and editor at The Dispatch, formerly of National Review. He is a friend of mine and others at NR, and you can take my review with a grain of salt — but when you read the book yourself, you will see how smart, sensitive, and valuable it is.

The phrase he uses in his title — “divided we fall” — is a familiar one. It is the second half of a longer phrase, “United we stand, divided we fall.” I will return to the concept of unity in a moment. French’s introduction is headed “The House Divided.” This comes from the Gospels, of course, and was used to powerful effect by Lincoln in the 1850s.

Originally, French wanted to title his book “The Great American Divorce.” That works too. (I think of a movie from the 1960s: Divorce American Style.)

How about the subtitle of the book? It’s “America’s Secession Threat and How to Restore Our Nation.” Is French serious about “secession threat” or is that just hyperbole? The threat is not imminent, he says, but not to be discounted. He intends his book to be a wake-up call.

“It’s time for Americans to wake up to a fundamental reality,” he says in the first sentence of his book: “The continued unity of the United States of America cannot be guaranteed.” In the last sentence of the book, he writes, “We cannot simply presume our national unity will last.”

I like the word “restore” in the subtitle: “restore our nation.” I like it better than “unite,” because when people talk about “uniting” the country, they usually mean on their terms: Become more like me. Do it my way. David French wants a pluralistic country — a patchwork — where people pretty much live and let live.

He is very well positioned to write this book, being bicultural, binational. I will explain.

French was born in Alabama and grew up in Kentucky and Tennessee. He went to Lipscomb University, a Christian institution in Nashville. So, that is all “red”: red America. Then he journeyed deep into “blue” America. He went to Harvard Law School; lived and worked in New York City; did the same in Philadelphia; and taught at Cornell.

He has a foot in each camp, and friends in each camp. He understands each camp — each world — from the inside.

“Bicultural” or “binational” though he is, French is a “son of the conservative movement,” as he says. He has been a Reagan man since he was 14. At Harvard Law, he started a pro-life group. He spent many years defending religious liberty, especially the rights of Christian students, discriminated against on their campuses. For years, he was an officer in the Army Reserve, and he served in the Iraq War. He received the Bronze Star. Asked how many guns he owns, he’ll give the Dick Cheney answer: “More than I need, fewer than I want.”

You might figure French for a conservative pin-up, and he was. But then came 2016 and the fractures over Donald Trump. French could not stomach Trump, and much of the Right came down on him — French, that is — like a ton of bricks.

The milder critics accused him of being a “Beltway insider” who craved invitations to “Georgetown cocktail parties.” In fact, French lives in Tennessee, in “the heart of Trump country,” as he says. As for Georgetown cocktail parties, he may have attended a few of those — having done most of his growing up in Georgetown, Ky.

Other critics were not so amusing. They heaped vile abuse on French and his wife, Nancy (who is also a writer). The Frenches received death threats. Their youngest child is a daughter, adopted from Ethiopia. This fact inflamed many of the critics, and threateners.

David French has faced bullies on the left as well — bullies and mobs. This was especially true in his career as a litigator. He has seen a lot: good, bad, and ugly.

To many of us, he is still a conservative pin-up — a model. But things are different for him now.

For the first time in my life, I’m a man without a party. I have no “tribe.” And I must confess that it has opened my eyes. I see things differently than I used to, and I understand the perspective of my political opponents better than I did before.

In his new book, French does no arguing for conservative positions, or liberal positions, for that matter. That is for other books, other occasions. He is focused on one concern: polarization — a polarization laden with enmity — and the danger it poses.

His book is organized into three sections. First, the problem, i.e., the divide — the two Americas. Second, how dissolution could occur. And third, how to prevent such a catastrophe.

French is doing his best to make an academic paper, written back in 1999, famous. He has cited it in his speeches for years, and he devotes a chapter to it in his book. He says that the paper “ex-plains America.” If there is one point in the book to understand, he says, it is the point of the paper.

What is this blockbuster piece of writing? “The Law of Group Polarization,” by Cass Sunstein, then of the University of Chicago Law School, now of Harvard Law. And what is its point? French boils it down to these simple words: “When people of like mind gather, they tend to become more extreme.”

And this extremism can lead to a lot more than nasty words on social media.

America has always known incidents of political violence — or incidents of violence broadly related to politics — even apart from our civil war. In the last few years, there has been one after another.

A shooting at a D.C. pizzeria, inspired by the “Pizzagate” conspiracy theory. The shooting at a congressional baseball game. The shooting at a synagogue in Poway, Calif., and another one at a synagogue in Pittsburgh (a mass murder). More mass murder at a Walmart in El Paso. Two months ago, a plot to kidnap the governor of Michigan.

People tend to know about violence inflicted on their allies, writes French. About violence inflicted on their opponents? They tend not to hear about that. Each side is well versed in its grievances, and only lightly aware, if aware at all, of the other side’s. “So the narrative builds,” writes French. They have wronged us, and we must fight for our lives. They are dangerous, and we are innocent.

In the middle section of his book, French imagines two “exits”: two withdrawals from the United States. A Calexit and a Texit. California and Texas, going their separate ways: one “blue,” one “red.” This results in “a world on fire,” as America’s foreign commitments fall apart, and the likes of China take advantage.

This section of the book is ingenious — French could write a novel — and unnerving.

All right, what to do? “To go forward,” writes French, “we must go back.” (That is a deeply conservative sentiment.) Back to what? To the American founding and its principles.

French dedicates his book to his wife, Nancy. And also to James Madison (“May we remember that you were right”).

The answer to our problems, according to French, and to his friend Madison, is pluralism. We don’t have to love one another (though that would be nice). We do have to live with one another (if only at a distance).

Everyone knows that the First Amendment protects individual liberty, or should know it. But we should also remember that it protects the right of association, says French: the right to form groups and communities that reflect distinct values.

And it’s this right of voluntary association that is the lifeblood of true pluralism. Its message to Americans of all races, religions, creeds, and sexual orientations is clear: Not only do you have a place in this society, it is a place secured even against the oppression of hostile majorities. You and your community can thrive in this American republic.

Related to pluralism is federalism: Let California be California, Texas be Texas; let Oregon be Oregon, South Carolina be South Carolina — with this caveat: The fundamental rights of every citizen must be protected.

“If you are a citizen of a pluralistic, liberal republic,” writes French, “you need to defend the rights of others that you would like to exercise yourself — even when others seek to use those rights to advance ideas you may dislike or even find repugnant.” Call it a golden rule, as difficult to obey, sometimes, as the original one.

Many will defend the baker who does not wish to customize a cake for a gay wedding. Many will defend the NFL kneeler. Will anyone defend both? French will, and has.

He asks his reader to “rediscover tolerance.” He also says that kindness should not be perceived as weakness. And that decency should not be treated as though it were cowardice. And that acts of grace should not be disdained as concessions to evil.

Reading this book, I thought of India, that storm of ethnicities, religions, and languages. America, by comparison, is homogeneous. If India can hang together, surely we can?

As you may remember, I’ve pooh-poohed the idea of uniting our country (an idea easy to pooh-pooh). Yet America can be united around one thing, says French: shared liberty. At the same time, liberty must be accompanied by rectitude, at least to a degree. Otherwise, the bad qualities of man will burst through the cords of our Constitution like a whale through a net.

The words come from John Adams, quoted by French.

Among the best qualities of man is courage — and French’s concluding pages are headed “A Call to Courage.” He talks about the liberal professor who will not speak out against illiberalism on campus, lest he be the next target of the mob. This is understandable, but what is tenure for? He talks about the D.C. Republican who will not say what he knows to be true, lest he get crosswise with Fox. This is understandable, too — but what do you have a voice for?

Incidentally, French observes that “Fox is far more ideologically diverse than, for example, the humanities faculty at virtually any academic institution of note.”

It is possible that David French’s worries in this book are overblown. That is better than underblowing them. In any event, I suspect that French has gauged things correctly. He has taken the temperature of the country and found it dangerously high.

French is a man of strong opinions, and strong convictions, and they are conservative ones. He argues for his positions in column after column, essay after essay. Mainly, however, he is on Team America. If I were a politician, engaging in politician’s rhetoric, I would say, “He is neither red nor blue but red, white, and blue.” Above all, French wants the “frame” to hold — the frame being the Declaration, the Constitution, the Gettysburg Address, and maybe apple pie (plus basketball, David’s No. 1 sport).

Divided We Fall is an impressive piece of political and social analysis. It is also an act of pure patriotism.