Hillary Clinton and Henry Kissinger: It's Personal. Very Personal.

The Clintons and the Kissingers regularly spend holidays together at a beachfront villa.

Henry Kissinger and Hillary Clinton receive the Germany Freedom Award in 2009.

At Thursday night's Democratic presidential debate, one of the most heated exchanges concerned an unlikely topic: Henry Kissinger. During a stretch focused on foreign policy, Bernie Sanders, the senator from Vermont, jabbed at former Secretary of State Hillary Clinton for having cited Kissinger, who was Richard Nixon's secretary of state, as a fan of her stint at Foggy Bottom.

"I happen to believe that Henry Kissinger was one of the most destructive secretaries of state in the modern history of this country," Sanders huffed, adding, "I will not take advice from Henry Kissinger." He referred to the secret bombing of Cambodia during the Vietnam war as a Kissinger-orchestrated move that eventually led to genocide in that country. "So count me in as somebody who will not be listening to Henry Kissinger," Sanders roared. Clinton defended her association with Kissinger by replying, "I listen to a wide variety of voices that have expertise in various areas." She cast her interactions with Kissinger as motivated by her desire to obtain any information that might be useful to craft policy. "People we may disagree with on a number of things may have some insight, may have some relationships that are important for the president to understand in order to best protect the United States," she said.

What Clinton did not mention was that her bond with Kissinger was personal as well as professional, as she and her husband have for years regularly spent their winter holidays with Kissinger and his wife, Nancy, at the beachfront villa of fashion designer Oscar de la Renta, who died in 2014, and his wife, Annette, in the Dominican Republic.

This campaign tussle over Kissinger began a week earlier, at a previous debate, when Clinton, looking to boost her résumé, said, "I was very flattered when Henry Kissinger said I ran the State Department better than anybody had run it in a long time. So I have an idea about what it's going to take to make our government work more efficiently." A few days later, Bill Clinton, while campaigning for his wife in New Hampshire, told a crowd of her supporters, "Henry Kissinger, of all people, said she ran the State Department better and got more out of the personnel at the State Department than any secretary of state in decades, and it's true." His audience of Democrats clapped loudly in response.

It was odd that the Clintons, locked in a fierce fight to win Democratic votes, would name-check a fellow who for decades has been criticized—and even derided as a war criminal—by liberals. Bill and Hillary Clinton themselves opposed the Vietnam War that Nixon and Kissinger inherited and continued. Hillary Clinton was a staffer on the House Judiciary Committee that voted to impeach Nixon, and one of the articles of impeachment drafted by the staff (but which was not approved) cited Nixon for covering up his secret bombing of Cambodia. In the years since then, information has emerged showing that Kissinger's underhanded and covert diplomacy led to brutal massacres around the globe, including in Chile, Argentina, East Timor, and Bangladesh.

With all this history, it was curious that in 2014, Clinton wrote a fawning review of Kissinger's latest book and observed, "America, he reminds us, succeeds by standing up for our values, not shirking them, and leads by engaging peoples and societies, the sources of legitimacy, not governments alone." In that article, she called Kissinger, who had been a practitioner of a bloody foreign-policy realpolitik, "surprisingly idealistic."

This Clinton lovefest with Kissinger is not new. And it is not simply a product of professional courtesy or solidarity among former secretaries of state, who, after all, are part of a small club. There is also a strong social connection between the Clintons and the Kissingers. They pal around together. On June 3, 2013, Hillary Clinton presented an award to de la Renta, a good friend who for years had provided her dresses and fashion advice, and then the two of them hopped over to a 90th birthday party for Kissinger. In fact, the schedule of the award ceremony had been shifted to allow Clinton and de la Renta to make it to the Kissinger bash. (Secretary of State John Kerry also attended the party.) The Kissingers and the de la Rentas were longtime buddies. Kissinger wrote one of his recent books while staying at de la Rentas' mansion in the Dominican Republic and dedicated the book to the fashion designer and his wife.

The Clintons and Kissingers appear to spend a chunk of their quality time together at that de la Renta estate in the Punta Cana resort. Last year, the Associated Press noted that this is where the Clintons take their annual Christmas holiday. And other press reports in the United States and the Dominican Republic have pointed out that the Kissingers are often part of the gang the de la Rentas have hosted each year. When Oscar de la Renta died in 2014, the New York Times obituary reported:

At holidays, the de la Rentas filled their house in Punta Cana with relatives and friends, notably Bill and Hillary Clinton, Nancy and Henry Kissinger, and the art historian John Richardson. The family dogs had the run of the compound, and Mr. de la Renta often sang spontaneously after dinner. First-time visitors, seeking him out in the late afternoon, were surprised to find him in the staff quarters, hellbent on winning at dominoes.

In 2012, the Wall Street Journal, in a profile of de la Renta, wrote:

Over Christmas the Kissingers were among the close group who gathered in Punta Cana, including Barbara Walters, Bill and Hillary Clinton, and Charlie Rose. "We have two house rules," says Oscar, laughing. "There can be no conversation of any substance and nothing nice about anyone."

A travel industry outlet reported that Vogue editor Anna Wintour was part of the crew that year. The Times described the house this way: "[T]hough imposing in the Colonial style, with wide verandas (and its own chapel on the grounds), [it] also had a relaxed feeling." Last April, the Weekly Standard noted that the Clintons had spent a week around the previous New Year's at Punta Canta and that Secret Service protection for the trip had cost $104,000. It was during this vacation that Hillary Clinton reportedly decided to run for president for the second time.

This gathering of the Clintons, the Kissingers, and the de la Rentas seems to occur most years. In 2011, de la Renta, a native of the Dominican Republic, told Vogue that he built this seaside estate so he could host his close friends, and he cited the Kissingers and Clintons as examples. "At Christmas," he said, "we're always in the same group."

The Clinton campaign did not respond to a request for comment. Neither did Henry Kissinger or Annette de la Renta.

When awarding herself the Kissinger seal of approval to bolster her standing as a competent diplomat and government official, Hillary Clinton has not referred to the annual hobnobbing at the de la Renta villa. So when Sanders criticized Clinton for playing the Kissinger card—"not my kind of guy," he declared—whether he realized it or not, he was hitting very close to home.