A 22-year-old participant in the Deferred Action for Childhood Arrivals program. (Bob Karp/AP)

Donald E. Graham is chairman of Graham Holdings and co-founder of the scholarship fund TheDream.us.

Reader, something awful is about to happen. And you may be able to help stop it.

Let us suppose you are driving across the United States on a trip. You come to a city of 700,000 people — a city the size of Denver. But this city is surrounded by barbed wire. A group of courteous law-enforcement people are in charge, and when you stop and speak to them, they explain that everyone’s life there is about to become much harder.

You ask why. An official tells you: “These people are to be punished. They will never be allowed to work again legally. They’ll have to subsist on whatever income they can get from off-the-books jobs.”

You wonder: “Did they commit a crime?” “No,” comes the answer. “Not one of them has been convicted of even a semi-serious crime.” So what did they do?

“Well,” says the official, “their undocumented parents brought them to this country 10 or more years ago, when they were, on average, 6 years old. So they grew up here, most of them assuming they were Americans, but they are here illegally. They can’t change their status, no matter how badly they want to. About 75 percent of people in the country think they should be allowed to stay, work and pay taxes, but no one can figure out a way to change the law.”

Is one party for them and one against them? “No, the president wants them to be citizens. Most Republicans would at least let them become legal. But the Republicans want other things as well. The Democrats want to help these people and have for years, but they want other things, too. And they haven’t found a way to split the difference.”

Of course, my hypothetical city is called DACA. And I’m not exaggerating. If Congress doesn’t act by March 5 — and most people are betting against their acting — all 700,000 DACA recipients will (gradually, over two years) lose their legal right to work.

We know what will happen if they lose that right. Their lives will be ruined. Not damaged, ruined.

How do we know? Because that was the world before the Deferred Action for Childhood Arrivals program.

Roberto Gonzales of Harvard University studied about 150 undocumented teenagers in Los Angeles for his book “Lives in Limbo.” He met them in high school and followed them for years.

Some wanted to go to college, some did not. Many did go. Some graduated. Some were valedictorians.

It didn’t matter. They all wound up in, essentially, the jobs of their parents. They did dangerous construction work, cleaned toilets, worked in the underground economy. No law-abiding employer could hire them.

And that is what will happen to today’s DACA recipients if DACA goes away and is not replaced.

But some DACA recipients are already college graduates. They are teachers, nurses, medical students, accountants. Many, many more of them are college students.

To force law-abiding employers to fire these young people is crazy. It is worse than crazy: It is cruel. This is one of our wonderful country’s occasional fits of cruelty toward people with no money and no votes — just decency, talent, brains and motivation.

Reader: Do what you can to stop this from happening. You have a representative and two senators (unless you are a D.C. resident like me). Call them and tell them they must not just say the right words, but cast the right votes, too. Tell them they must compromise, even if it means they might face a primary challenge from some purist (and tell them you’ll round up your friends and support them in such a case).

Tell them not to ruin 700,000 lives for nothing.

If they tell you this all will be easily fixed in the future, remind them that the Dream Act was introduced in 2001.

It has never passed.