EYEWITNESS On June 13, 2018, Jacob Soboroff, a correspondent for NBC News and MSNBC, prepared to visit Casa Padre, a former Walmart in Brownsville, Texas, where nearly 1,500 migrant boys, ranging in age from 10 to 17, were living after being apprehended at the U.S.-Mexico border. Hundreds of them had been separated from their parents as a result of the Trump administration’s zero tolerance immigration policy. Journalists were not allowed to bring cameras inside the facility, so Soboroff stopped at Walgreens to buy a small blue spiral-bound notebook (along with a car charger, dry shampoo and yellow Gatorade, which calms his nerves).

Once he was inside the 250,000-square-foot building, Soboroff started jotting notes: “kids everywhere, oreos, applesauce, smile at them — ‘they feel like animals in a cage being looked at.’” This last bit was advice from Casa Padre’s chief programs officer and legal counsel, dispensed when Soboroff expressed amazement at what he was seeing — five cots per bedroom, kids watching “Moana” in a loading dock, a mural of President Trump accompanied by a quote: “Sometimes losing a battle you find a new way to win a war.”

Those notes — and Soboroff’s subsequent reporting — became the springboard for his first book, “Separated: Inside an American Tragedy,” now No. 14 on the hardcover nonfiction list, which traces planning for family separation back to March 2017. “It was a difficult story as a journalist and as a human being because there is so much trauma,” he says. “I realized right away, the night I left Casa Padre: It will never leave me.”

Soboroff has two children who kept him grounded while he worked on the book in a laundry room that doubles as a home office and now as a broadcast studio. (“A light fell on me about 30 seconds before we were going on the air, but I avoided catastrophe.”) At one point, in the midst of a move from a rental into his current home, Soboroff lost track of the blue notebook. He says, “I’m a disorganized person and I’m not used to working in that medium. I didn’t think of myself as a writer; I’m a TV guy.” Eventually he located the “memo book,” as it says on the cover, in a 5-by-10-foot storage unit, sandwiched between camping equipment, a pendant lamp and a baby changing table. Soboroff describes this moment in his book: “The notebook burned in my hand. … I barely needed to read a word to bring back the sights and sounds and feelings of being there.”