WASHINGTON — President Franklin D. Roosevelt never kept a diary. He never gave lengthy interviews to historians. He died before he had a chance to write a memoir. Yet he held the nation’s top office at a time of amazing tumult and transition.

Now historians have a new set of documents to help piece together the details of the nation’s longest presidency — and one of its most momentous.

The Grace Tully Archives, a collection of papers preserved by Roosevelt’s longtime secretary, were unveiled on Wednesday, weeks after legislation took effect that moved them from private hands to the National Archives.

Among them: the first draft of Roosevelt’s “Day of Infamy” speech, which Roosevelt dictated to Tully in the hours after the Japanese attacked Pearl Harbor on the morning of Dec. 7, 1941.

There’s also personal correspondence: Roosevelt musing about the creation of Social Security in 1935; Italian dictator Benito Mussolini’s request for a meeting to “discuss the outstanding world problems,” a letter from Ambassador to Great Britain Joseph P. Kennedy in 1939 a month after war had started in Europe.

For a man who “never completely confided in anyone, including his wife,” the documents are a treasure trove, said David S. Ferriero, the archivist of the United States.

“They help fill gaps in the record of a presidency that changed America,” Ferriero said. Because Roosevelt didn’t have many close confidants, “We have only a few records of what he was thinking, much of it in correspondence, notes he made to staff and even on speech drafts or memos sent to him.”

“You have to picture what it was like in eastern Kentucky before Franklin Roosevelt was president,” said Rep. Louise Slaughter, D-N.Y., who helped sponsor the legislation that brought the documents to the archives and who was born in 1929 in the poverty stricken coalfields of that region.

“Every year the rivers flooded, wiping out all the crops. Children died of typhoid. There was no electricity,” Slaughter recalled. “Since the Civil War era, the American South had continued to be punished until Franklin Roosevelt became president, and then he consciously helped rebuild that part of his nation. ... There was not a family in any part of the area I grew up in that didn’t think of him as a member of the family.”

Tully was working for the Democratic National Committee in 1928 when she was assigned to Eleanor Roosevelt, who was helping organize support for Al Smith, the Democratic nominee for president. When Franklin Roosevelt was elected New York governor, Tully was hired as an assistant to Marguerite “Missy” LeHand, Roosevelt’s personal secretary.

A year after Roosevelt was elected president in 1932, Tully moved to Washington to help LeHand. When LeHand became too ill to work in 1941, she took over as Roosevelt’s principal secretary. She was with Roosevelt when he died at Warm Springs, Ga., on April 12, 1945, the only man elected president four times.

Fortunately, to use the words of Anna Roosevelt, FDR’s granddaughter, LeHand and Tully were “packrats,” saving everything and preserving it, even after Roosevelt’s death.

“We need those types of people,” Roosevelt said. “Prior to the establishment of presidential libraries, papers were scattered to the winds.”

The papers entered a kind of limbo after Tully, who went on to be secretary to Democratic Sens. Lyndon Johnson of Texas and Mike Mansfield of Montana, died in 1984. Her sister held on to them for a while. Then they apparently were held by family friends before being auctioned off in New York to a rare book dealer, who bought them for $3.5 million and prepared to resell them.

That’s when the Franklin D. Roosevelt Presidential Library in Hyde Park, N.Y., became aware of them, but not before they were bought for $8.5 million by Hollinger International, the company that published the Chicago Sun Times and whose chairman, Conrad Black, was a collector of Roosevelt memorabilia.

In 2004, after Black was forced out amid allegations of defrauding investors that later led to a high-profile trial and conviction, the Sun Times asked the New York auction house Christie’s to sell them again. That’s when the National Archives realized they were presidential papers that should be housed at the FDR library.

The Sun Times allowed the papers to be boxed and sent to the library, but talks for a formal donation lasted until 2009, when the Sun Times filed for Chapter 11 bankruptcy and the papers were sold to the Chicago Newspaper Liquidation Corp.

Black was released from a Florida prison on July 21 on $2 million bond.

Sen. Charles Schumer, D-N.Y., introduced legislation granting a tax break in return for the papers’ being deeded to the archives. President Barack Obama signed it on Feb. 1, and the deal was closed on June 30.

“Five years, dozens of man hours, a handful of congressional votes and one presidential signature — all to remove the top of a box that had been sitting at the FDR library the entire time,” Schumer said. “It’s hard to believe it took a presidential signature ... to get this done.”

FDR Library Director Cynthia Koch said she hoped the documents — about 5,000 in all — will be available online by January. “They promise a window into FDR’s working life,” she said.

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