Former Secretary of State Henry Kissinger, who has counseled numerous American presidents and statesmen since he left government in early 1977, is back in the halls of power once again. Since the election, he’s positioned himself close to Donald Trump, advising the president-elect on key appointments and praising him in public. And Kissinger, who has maintained close ties to Russian President Vladimir Putin, is now positioning himself as an intermediary between the Kremlin and the incoming Trump administration.But previously undisclosed documents that I discovered while poring through the archives at Stanford’s Hoover Institution should give us serious pause about Kissinger’s resurgence. The storied former diplomat is not above using his considerable foreign policy credibility to further his private objectives, even to the detriment of the U.S. national interest. Indeed, on at least one occasion since he left public office, Kissinger used his influence with foreign leaders—in this case, the Pinochet regime in Chile—to undermine his domestic political opponents, including a sitting president of the United States.It all began on September 21, 1976, when, during the final months of the Gerald Ford administration and Kissinger’s tenure as secretary of state, Chilean President Augusto Pinochet ordered the assassination of Orlando Letelier, a prominent Chilean dissident and former ambassador to the United States who was then working at a think tank in Washington, D.C. At 9:30 a.m. on that drizzly Tuesday, a group of Cuban anti-communist extremists allied with Pinochet’s intelligence services detonated a remote-control bomb placed on the underside of Letelier’s Chevrolet while it rounded Sheridan Circle—a 20-minute walk from the White House. Letelier and his American co-worker, Ronnie Moffit, were killed in the explosion. The first known act of state-sponsored terrorism ever to take place in the American capital, the assassination and its aftermath were national front-page news for years. Investigators and prosecutors tried to crack a case that took them across three continents, all while facing significant pushback from elements within the U.S. government who preferred not to rattle Cold War alliances.In August 1978, after a long and tortuous investigation, U.S. federal prosecutors indicted three Chilean intelligence agents for masterminding the assassination, including the former head of Pinochet’s intelligence services, Manuel Contreras, and his director of operations, Pedro Espinoza. In a shocking repudiation of a major American ally in the hemispheric battle against communism, President Jimmy Carter’s administration formally requested that Chile extradite the three men to the U.S. to stand trial.By 1979, the Letelier case threatened to sour relations between the U.S. and the Pinochet government. On October 1, 1979, the Chilean Supreme Court, intimidated by members of the Chilean military (and a bombing campaign targeting the judiciary), rejected the U.S. government’s extradition request. Carter equivocated about how hard of a line to take with Chile in response. U.S. liberals wanted the president to break diplomatic relations entirely; staunch anti-communists were far more forbearing toward Pinochet, who had become president after a coup that Kissinger had helped orchestrate as national security adviser, overthrowing the democratically elected Marxist Salvador Allende.That was when Kissinger, then a private citizen, decided to weigh in. Two days after the Chilean high court rejected the U.S. demand for extradition, Kissinger hosted Chilean Foreign Minister Hernan Cubillos at his longtime Manhattan residence, the River Club.Over a 70-minute-long breakfast, the two men embarked on a wide-ranging discussion, all detailed in an extraordinary memo Cubillos wrote after the meeting and that I discovered in Cubillos’ personal papers at the Hoover Institute archives. According to the record, which the foreign minister sent as a high-level secret diplomatic cable back to Chile, they discussed the recent election of Pope John Paul II (Kissinger was “not completely convinced he will be good for humanity”); Carter’s recent speech on Cuba (which Kissinger called “a disaster”); and Kissinger’s forthcoming memoirs (which the former secretary of state said would “cause great discomfort among liberal circles”). Kissinger denigrated certain prominent State Department officials as “stupid” and “fanatical,” and offered Cubillos advice on whom to lobby in D.C. and New York to improve U.S.-Chilean relations. The Carter administration’s treatment of the Pinochet regime was “a disgrace,” he said. (Kissinger did not respond to requests for comment.)According to Cubillos’ recounting, the two men also discussed the Letelier case extensively. First, Kissinger told Cubillos he believed that the Chileans made the “correct” decision in rejecting the U.S. government’s extradition request. And then, Kissinger went on to advise the Pinochet regime on how to get what he wanted from Carter. You have to be tough, he told Cubillos—in fact, you must treat the Carter administration “with brutality.” This, Kissinger said, “is the only language they understand.” This was no idle slip of the tongue; according to Cubillos, Kissinger “repeated this same idea several times during the conversation.”Kissinger then said that Chile would not be able to improve its relations with the U.S. until after the 1980 election, when he believed that the Republican Party (more specifically either Gerald Ford or John Connally) would win the presidency. Until a friendlier regime took power in Washington, Kissinger advised, Chile needed to hold firm.As the meeting ended, Cubillos invited Kissinger to visit Chile, and Kissinger volunteered to continue the conversation through the Chilean ambassador in Washington. All in all, Cubillos wrote, his meeting with Kissinger was a “fruitful and interesting” one.Indeed, after this fruitful meeting, Cubillos travelled to the U.S. Mission to the United Nations in New York to meet with State Department officials, including Secretary of State Cyrus Vance, later that same day. In yet another memorandum I discovered at the Hoover Archives, Cubillos recounted the difficult conversations he had with different U.S. officials about the extradition case, some of whom chastised Cubillos harshly over Chile’s unwillingness to turn over the three officials. In the memo, sent back to Chile as a secret telegram, Cubillos noted how his conversation with Vance “confirms the positive assessment” Kissinger gave of Vance during their conversation that morning. (According to Cubillos, Vance even told him he would “try to reduce the pressure” over the case.)***In November 1979, the Carter administration announced that it would punish Chile for its intransigence by banning trade assistance to the country through the Export-Import Bank. This was a far weaker response than many had hoped for, given the seriousness of the crime, and the thoroughness of the obstruction on the part of the Chileans. For another decade, the Pinochet regime remained implacably opposed to extraditing those responsible for the killing. (When democracy returned to Chile in 1990, however, both Contreras and Espinoza were eventually given long jail sentences for their crimes.)There are those—including me—who believe that Carter should have reacted more forcefully to Chile’s refusal to extradite those responsible for Letelier and Moffit’s murder. Extradition of the three Chileans, if it had been successful, would have provided a powerful deterrent to other state actors considering financing or sponsoring acts of terrorism in the United States, or those considering attacks on U.S. targets abroad. And it would have signaled the lengths to which the U.S. government was willing to go in order to bring terrorists to justice.Still, there were and are those who believed the opposite. Kissinger might genuinely have believed that the Carter administration had committed a geostrategic error by conducting a thorough murder investigation into high-ranking military officials in a friendly anticommunist regime. And he might genuinely have believed that Chile’s complying with the request would further destabilize a crucial alliance; after all, one of the indicted co-conspirators, Contreras, had previously even served as a CIA informant. There were close, if covert, ties between the two countries. But the breakfast with Cubillos was never as simple as an unofficial, frank conversation. Hanging over the whole discussion was the unspoken implication that Kissinger himself might soon regain his old job as secretary of state, where he would once again be in charge of shaping U.S. foreign policy towards Chile. Ford, whom Kissinger predicted (incorrectly) would win the presidency in 1980, had remained close to his former top diplomat. (In fact, at the 1980 Republican Convention, Kissinger led a team of Ford loyalists in negotiations with the Ronald Reagan camp. The deal, which would have brought Ford back as vice president in an unusual power-sharing arrangement, would have returned Kissinger to his position at state.) By October 1979, Cubillos very likely believed that Kissinger was on the cusp of a comeback. And the Pinochet government also knew that relations would improve if a Republican were elected president. (Indeed, according to the American ambassador to Chile at the time, members of the Chilean military danced in the streets upon news of Reagan’s electoral victory. And in 1981, against the howls of liberals, Reagan lifted Carter’s trade restrictions. Pinochet remained president for nine more years.) There is also no doubt that Kissinger, and the Republican Party more broadly, stood to benefit from the sort of Chilean intransigence that Kissinger urged on Cubillos. Greater cooperation by Chile in the case could have handed the Carter administration a major diplomatic victory during a period of great economic and political turbulence. In other words, whether or not Chile’s compliance with the extradition request was in our national interest, it was certainly not in Kissinger’s. And in his icy, amoral advice to the Chilean government, he definitively showed whose interests he was most concerned with.Consider, too, how inappropriate, how borderline subversive, Kissinger’s counsel to Cubillos was. Not only did he laud Chile’s decision to stymie a murder trial related to a major act of international terrorism carried out in the U.S. capital, but the former secretary of state also actively encouraged the regime ostensibly responsible for that crime to take a hard line with the U.S. government, in order to further stonewall U.S. prosecutors—that is, the Justice Department.To the best of my knowledge there has never, before now, been proof of Kissinger’s secret interference in U.S. politics after he left public service. The paper trail for Kissinger dries up; there are no more U.S. government documents subject to declassification. Indeed, we know very, very little about Kissinger’s political affairs after 1977. Since 1983, he has run an international consulting firm, Kissinger Associates, that has facilitated contacts between major corporations and a number of authoritarian regimes. During much of this time, he or other members of Kissinger Associates have sat on the President’s Intelligence Advisory Board, a little-known civilian panel tasked with intelligence oversight duties where members have access to highly classified data.What, then, has Kissinger been advising corporate clients or representatives of foreign governments behind closed doors since 1977? Has his counsel been in the best interests of the United States? At least in the case of Letelier and Moffit—in bringing to justice the perpetrators of one of the most audacious acts of terrorism ever conducted on American soil—the answer is a resounding, and disquieting, no. And if the Letelier case is part of a larger pattern, we should be extremely circumspect about Kissinger’s private intercession in our country’s public affairs today.