John F Kennedy’s secret talks with Soviet intelligence, surreptitious tape recordings and “girlfriend system” create a new portrait of a cunning and cagey JFK, according to a historian who has researched a treasure trove of recently released recordings and papers of the late president.

Drawing on documents and tape recordings recently declassified, historian Timothy Naftali told a meeting at New York University on Tuesday night that Kennedy’s wife Jacqueline and brother Robert censored and edited the president’s legacy, cultivating the “mystique” of a charismatic leader who continues to baffle and fascinate Americans of all stripes and creeds.

Conservatives, liberals, conspiracy theorists and people who write “what if” histories fight over him. Fans of Bernie Sanders compare their candidate to him. A Fox News pundit wrote a children’s book about him. More than 25 years ago, author Don DeLillo addressed JFK mania indirectly and concluded: “Facts are lonely things.”

Naftali has attempted to answer some old questions with a new angle, arguing that the new details of what Kennedy did behind the scenes reveal a secretive yet self-indulgent president whose family was as worried about image as the man himself.

Kennedy was “far more interesting intellectually and far less appealing personally” than his family and friends wanted the world to know, Naftali told the Guardian. “And that’s fine.”

Backroom deals reveal JFK as a cold war skeptic rather than a hawk, Naftali said, though the president never lost sight of necessary theatrics.

From 1961 through the Cuban missile crisis, for instance, Kennedy sent his brother Robert to hold secret talks with Soviet spy Georgi Bolshakov. Recordings also reveal that Kennedy decided to pursue negotiations against the advice of his cabinet, and with his brother’s help.

But to preserve his image, according to the historian, Kennedy leaked a “cockamamie” story that made Adlai Stevenson, his ambassador to the UN, “look like a chump” for any concessions to the Soviet Union.

“He did not believe ‘bear any burden, pay any price’,” Naftali said. “But he wanted to be a politician, he wanted to be liked.”

Similarly, Naftali said that Kennedy did not want to order the disastrous 1961 Bay of Pigs invasion of Cuba, but felt “boxed in” by politics, feeling the need to prove he was against Fidel Castro, who was courting Soviet aid while taking over American holdings on the island.

Kennedy “was making re-election decisions”, Naftali said. “He thought Americans didn’t have the political courage” for diplomacy with communist countries.

President Kennedy, right, meets the Soviet foreign minister, Andrei Gromyko, second from right, and other Soviet officials in the Oval Office on 18 October 1962. Photograph: AP

Naftali said the episode had at least some relevance to Barack Obama’s four-year dilemma over the Syrian civil war, in which an autocratic leader similarly defied an American warning about military intervention.

“JFK had drawn a line. Drawing lines is just trouble,” Naftali said. Obama also drew a “red line” against Bashar al-Assad’s use of chemical weapons, but then failed to act to enforce it militarily when the Syrian leader was found to have used such weapons.

Other famous cold war episodes were also tentative steps toward detente, he added. A year after he called on Americans to land on the moon, for example, Kennedy asked the Soviets, in private and in public, to join with the US and conquer space together. Similarly, Kennedy was worried about the collapse of Laos and tried to work with the Soviets to resolve tensions there, Naftali said.

Kennedy’s penchant for secrecy extended well into his personal life. Even friends did not know Kennedy well, Naftali said, and the president kept a hidden tape recorder in his office unbeknown to almost everyone. Aides also arranged what Naftali called “the girlfriend system” to ferry women in and out of his chambers.

White House marginalia offer new clues about Kennedy’s philandering, which has been well documented and speculated upon for decades. Logs show that Jackie Kennedy was almost never with her husband on Friday nights, Naftali noted, and flight manifests sometimes list a 19-year-old White House intern, Mimi Beardsley, alongside all the president’s men.

“Who is this intern who gets placed on a plane before anybody else?” Naftali asked, saying the lists confirm Beardsley’s stories of sleeping with the president.

The president watches his children Caroline and John F Kennedy Jr playing in the Oval office. Photograph: -/EPA

Kennedy created a “culture of secrecy” that would have eventually haunted him, Naftali said. That he spoke candidly only with his family, recorded hundreds of hours of conversations with unwitting people, and quickly resorted to intrigue – as with a CIA-backed coup in South Vietnam – “compounded the secrecy in the way he dealt with the world”, Naftali said.

Kennedy and his family actively erased less palatable versions of events, documents show, including the role played by Kennedy’s father, Joseph Kennedy, whom Naftali called “an arch-conservative” with a Wall Street fortune, a womanizing habit and unpopular opinions about the Nazis. But he said the patriarch was “a player in this administration” nonetheless, and call logs show that Kennedy called his father repeatedly during the height of the Cuban missile crisis.

Similarly, Kennedy’s brother and wife tried to erase personal blemishes – about his affairs, sense of entitlement, guardedness – after his assassination in 1963, as evinced by the deed granting them rights to control what papers the government received, and by their edits of biographers’ work. “The Kennedy they wanted was boring,” Naftali said.

“He was a very ambitious and talented rich kid,” he said. “He was also tough, and a war hero, but he was indulged.”

He added the personal flaws were important: “The self-indulgence doesn’t creep into his policy but it shapes the White House.”

Finally, Naftali touched on another famous mystery: the president’s rocky relationship with his vice-president, Lyndon B Johnson, who was caught up in a corruption scandal in the weeks before Kennedy’s assassination.

Lyndon Johnson takes the oath of office on board Air Force One after President Kennedy’s assassination. Kennedy may have been planning to drop Johnson from the re-election ticket. Photograph: Cecil Stoughton/Corbis

“LBJ’s brand was on the verge of collapsing,” Naftali said. Citing notes taken by the president’s secretary, he said he suspected Kennedy wanted Johnson off the re-election ticket. “I think Kennedy wanted LBJ to retire off the ticket.”

This healthy dose of speculation was welcomed by the audience at New York University, which included more than a few people who preferred their own theories to the historian’s. A clinical psychologist declared that JFK “was obviously a sex addict”, adding: “What about his father, and also this thing with the mafia?”

Naftali demurred. “I’ve gone through each of the conspiracies one by one, trying to line them up, and could just never make that jump,” he said. “I believe it was Lee Harvey Oswald [who killed Kennedy].”

Danyal Sadiq, an assistant to a former Kennedy aide, wanted to talk to the professor less about conspiracy than legacy, saying that too many Americans see “the style more than the substance” of JFK. “He’s been overshadowed by the glamour and rumors and celebrity.”

Sadiq, students and septuagenarians crowded the historian anyway, eager to talk about the mysteries that have spawned an ever-growing industry of interpretations and analysis, to which Naftali hopes to add his book in 2017, which marks 100 years since JFK’s birth.