Story highlights A surprise guest gate crashed Thursday's Democratic debate: Henry Kissinger

The former foreign policy guru to President Richard Nixon took an unexpected, starring role in an exchange between Bernie Sanders and Hillary Clinton

(CNN) A surprise guest gate crashed Thursday's Democratic debate: Henry Kissinger.

In a blast from the 1970s that must have left many young Democratic voters bewildered, the former foreign policy guru to President Richard Nixon took an unexpected, starring role in an exchange between Bernie Sanders and Hillary Clinton.

Kissinger won a Nobel Peace Prize for helping to arrange the end of U.S. involvement in the Vietnam War, and is credited with secret diplomacy that helped Nixon open Communist China to America and the West.

But he is reviled among many liberals over the bombing of Cambodia during the Vietnam War that led to the rise of the genocidal Khmer Rouge movement and over claims he backed a coup against a democratic government in Chile.

Sanders called on the old Cold Warrior to make the case that despite her claims to be the most qualified Democrat to serve as the next president, the more hawkish Clinton is out of tune with her party on foreign policy and national security.

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