Watch: Hillary Clinton and Bernie Sanders get into it over...Henry Kissinger?

Near the end of Thursday's Democratic debate, Bernie Sanders launched into a new attack on Hillary Clinton: her embrace of former US Secretary of State Henry Kissinger, — a controversial figure to say the least. He's been ranked by some the the most effective secretary of state in American history and by others as a war criminal.

In the debate, hosted by CNN and PBS, Clinton cited praise from Kissinger as evidence that she'd make for a good president. Sanders hammered her for it, saying "I happen to believe that Henry Kissinger was one of the most destructive Secretaries of State in the modern history of this country."

He went on to say:

[Clinton] talked about getting the approval or the support or the mentoring of Henry Kissinger. Now I find it kind of amazing: Because I happen to believe that Henry Kissinger was one of the most destructive secretaries of state in the modern history of this country.

I'm proud to say that Henry Kissinger is not my friend.

I will not take advice from Henry Kissinger. And in fact, Kissinger's actions in Cambodia, when the united States bombed that country, over -- through Prince Sihanouk, created the instability for Pol Pot and the Khmer Rouge to come in who then butchered some 3 million innocent people – One of the worst genocides in the history of the world. So count me in as somebody who will not be listening to Henry Kissinger.

Clinton hit back, with a pretty sick — and quite true — burn, referencing Sanders' campaign's inability to name a principal foreign policy adviser: "Well, I know journalists have asked who you do listen to on foreign policy and we have yet to know who that is."

To which Sanders then responded: "Well, it ain't Henry Kissinger, that's for sure."

It was an entertaining exchange, and also one of Bernie's finest debate moments on foreign policy to date. Sanders' previous foreign policy arguments tended to be limited to "noun, verb, 2002 Iraq war," but tonight seemed different.

Here he demonstrated a breadth of knowledge on US foreign policy that had, so far, been sorely lacking. Moreover, he demonstrated an ability to latch onto a foreign policy issue that some parts of the Democratic base cares about — America's long tradition of doing horrible things to people in foreign countries, like Cambodia — and using it against Clinton. Her defense made her sound like an insular member of the DC elite.

It's the kind of attack he's deployed effectively on domestic policy, but hadn't really managed to pull off that well thus far on foreign policy. This was an improvement, even if the vast majority of Democratic voters aren't going to change their minds based on a debate over a guy who hasn't held a public position for 40 years.