It was the most contested election in the history of Texas. On August 28, 1948, Lyndon B. Johnson, a ruthless young Texas congressman, squared off against former Governor Coke Stevenson in a brutally competitive runoff for the U.S. Senate. In the chaotic days following the election, Stevenson appeared to be victorious. STEVENSON’S MARGIN FIRM, blared The Dallas Morning News five days after the polls closed.

But election officials received an amended return from Jim Wells County, a backward region in south Texas, which showed two hundred additional votes for Johnson. Those votes put Johnson ahead of Stevenson, and eventually guaranteed his victory by eighty-seven votes. Pundits would later refer to “the eighty-seven votes that changed history”- votes that came from Precinct 13 in Alice, Texas. The election judge for Precinct 13 was a burly, belligerent pistolero named Luis Salas, a top lieutenant to the “boss of bosses” in Jim Wells County and a political ally of Lyndon Johnson. Salas stole the votes.

In 1986 Robert Caro, hard at work on volume two of his projected four-volume biography of Lyndon Johnson, ventured to southern Texas in search of Luis Salas. The elderly men in the streets of Alice told him that Salas was deceased, but eventually someone exclaimed: “No, Luis is alive. ” After several weeks of scouring telephone books, Caro found Salas in the Houston suburbs, where he was living in a mobile home in the backyard of his daughter’s house. The author knocked on the door. Caro recalls: “It was just like he was expecting me.”

Caro was greeted by an eighty-fouryear-old man, frail and withered, who bore no resemblance to the thug he had read about in old newspaper clippings. “Mr. Salas, my name is Robert Caro. I’m doing a book on Lyndon Johnson.” “Oh,” Salas replied, “then you want to know about Box 13.” They sat on a couch in the trailer. Salas’s ailing wife languished in an adjacent room, and Caro has never forgotten the old man’s tenderness toward her. With regard to the 1948 election, Salas announced: “I have written it all down,” at which point be produced a battered, typed and handwritten manuscript that revealed, in striking detail, the machinations surrounding Box 13. The two men went to a stationery store and made a Xerox copy. Caro thanked him. “Everyone is dead except me, Robert,” Salas remarked. “And I’m not going to live long. But Box 13 is history. No one can erase that.”

By obtaining the firsthand recollections of the man who actually stole the crucial votes in the 1948 Texas Senate race—and thereby set Lyndon Johnson on the road to the presidency—Caro achieved a stunning journalistic feat. For years, Johnson’s partisans had worked to create an obfuscatory haze around LBJ’s chicanery in that election; but the Salas manuscript is the closest thing we have to a smoking gun.

It was vintage Caro. Beginning at Newsday in the 1960s, Caro has forged a reputation as an indefatigable muckraker, a man whose tenacious research and indepth reporting have enabled him to produce books that are acclaimed by his peers and celebrated by his readers, books that leap to the top of the best-seller lists. His first book, The Power Broker: Robert Moses and the Fall of New York, was awarded the Pulitzer Prize and continues to sell briskly a quarter century after its publication. Since then, Caro has dedicated himself to a massive biographical project on LBJ, a project dubbed The Years of Lyndon Johnson. The first book in the series, The Path to Power (1982), covered LBJ’s life until 1941. Means of Ascent (1990) tracked Johnson from 1941 to 1948. The third volume, Master of the Senate, has just been published, at nearly twelve hundred pages.

In some influential journalistic quarters, Caro’s infallibility is simply assumed. In a recent New York Times article concerning the plagiarism controversy swirling around the historians Stephen Ambrose and Doris Kearns Goodwin, the publishing columnist Martin Arnold wrote: “As for today’s popular historians, no one would waste a moment checking Robert A. Caro, who invests years in researching and writing each of his books.”

Yet the praise for Caro is not unanimous; his work is controversial and contested. The sides are clearly drawn. Firmly in Caro’s corner are two of the most powerful institutions in American literary life: Alfred A. Knopf, his publisher, which is promoting Master of the Senate as “the most celebrated political biography of our era,” and The New Yorker, which recently ran two long excerpts from Master of the Senate.

Scott Sherman is a contributing writer at The Nation and a contributing editor at the Columbia Journalism Review.