After months of bizarre non-debate over foreign policy in the Democratic primary, in which Bernie Sanders appeared alarmingly uninterested in even the very basics of foreign affairs and Hillary Clinton was able to dominate the issue despite being to her party's right, the two candidates finally had a substantive foreign policy debate on Thursday night. And it was pretty revealing.

Sanders is still much weaker than Clinton on foreign policy; he still has little in the way of policies and can't even name one adviser on the subject. But he appears to have finally studied up enough to at least discuss the issues and try to position himself against Clinton.

As a result, we finally got some glimpses into the differences between the candidates on how they see, and how they would institute, one of a president's most important roles. Here's what we learned.

1) Hillary Clinton really does have a Henry Kissinger problem

The most memorable exchange on foreign policy came when Sanders finally called out Clinton for her habit of name-dropping Henry Kissinger, the former secretary of state and war criminal.

"I happen to believe that Henry Kissinger was one of the most destructive secretaries of state in the modern history of this country," he said. "I'm proud to say that Henry Kissinger is not my friend."

Alex Pareene of Gawker articulated this problem well: It's not that Clinton is insufficiently critical of, say, Kissinger's 1969 Cambodia bombings, but rather that she is so ensconced in the world of Beltway elite bipartisan consensus that she believes Kissinger's support will be both positive and uncontroversial.

Sanders, in calling this out, forced Clinton to either disavow Kissinger or defend him — giving us useful insight into how she thinks about him and his legacy. And she chose to defend him, citing his expertise on China.

"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 during her mostly rambling answer.

Every time she was challenged, Clinton retreated into technocratic recitations of minutiae

This is a real problem for Clinton. It shows that she is too isolated within the bubble of old-guard foreign policy elites who have never bothered to learn from or even confront their own mistakes — including not just those of Kissinger in Cambodia, but also more recent mistakes such as the 2003 invasion of Iraq, which Clinton supported.

If Clinton exists in a world where Kissinger's mistakes aren't serious enough to even reconsider name-dropping him on the campaign trail, one has to wonder just how much she learned from more recent American-made disasters like that of Iraq.

2) Sanders's greatest strength and weakness: his obsession with Cold War lessons

One of the mysteries of Sanders's prior inability to discuss foreign policy is that earlier in his career, he was highly engaged on foreign policy issues. How to square the younger Sanders's well-known passion for foreign policy with present-day Sanders's near-total disengagement?

It turns out we now have the answer: Sometime during the 1980s, when he was mayor of Burlington, Sanders shifted abruptly and totally away from the world affairs that had fascinated him up until that moment, and hasn't really thought about them since.

Hearing Sanders discuss foreign policy was like listening to someone who had been cryogenically frozen in 1983 and thawed out mere moments before walking onto the stage

Last night Sanders gave us extended lectures on the dangers of the domino theory, the 1953 US-backed coup against Iranian leader Mohammad Mosaddegh, and US policy toward Cambodian leader Norodom Sihanouk. The past leaders he name-checked — Teddy Roosevelt, Franklin Delano Roosevelt, Herbert Hoover, and Winston Churchill — were all contemporaries of the Ottoman Empire.

There is something refreshing and indeed important in Sanders recalling the long-forgotten lessons of the mid–Cold War era. Americans are not very good at remembering our mistakes, and Sanders is correct to raise those lessons, particularly the dangers of regime change, in how they apply today. (Though one wishes Sanders would catch up to at least the late Cold War, where he could learn about the even-more-applicable dangers of arming extremist militias to serve US aims.)

But even if he had, learning the lessons of American foreign policy from 1950 to 1980 is not remotely sufficient for understanding how to confront the challenges of today. The world has changed pretty significantly in the past few decades, and I'm not just thinking here about the rise of apocalyptic Salafist jihadism. Failed states now threaten the US in a way they never could 20 years ago. Russia has developed a new form of warfare, hybrid war, to which we are struggling to find an answer. The stability of the European Union is in question.

Hearing Sanders discuss foreign policy at Thursday's debate was thus like listening to someone who had been cryogenically frozen in 1983 and thawed out mere moments before walking onto the stage. Republicans sometimes talk as if the Cold War never ended; Sanders seemed at points legitimately unaware that it has. That is concerning for his ability to confront a very new and different set of challenges.

3) Sanders wants to make the contest about principles versus experience

That's an effective strategy for him — it's not going to make him the dominant foreign policy candidate, but it can at least help him even out a contest where he previously looked hopelessly lost — and Clinton doesn't yet have a good answer to it.

The key moment came in the candidates' exchange over Kissinger, when Clinton tried to deflect with a line that has worked for her in the past: pointing out that Sanders has no foreign policy to speak of. Finally, he was ready with an answer: At least I'm not part of the pro-war establishment.

Sanders: So count me in as somebody who will not be listening to Henry Kissinger. Clinton: Well, I know journalists have asked who you do listen to on foreign policy and we have yet to know who that is. Sanders: Well, it ain't Henry Kissinger, that's for sure.

This exchange validates the feelings of both candidates' supporters: Sanders supporters will like his rejection of the establishment, and Clinton supporters will appreciate her show of expertise. In political terms, it was a tie.

But even a tie is a small victory for Sanders, because foreign policy was an issue on which Clinton has previously dominated. He pulled it off not by trying to challenge Clinton's experience or expertise but by demonstrating a bare minimum knowledge of current events — he name-checked a few countries to show us he could at least recognize a map of the Middle East — and then arguing that he has superior judgment.

"Judgment matters as well," Sanders said, presenting himself as having a superior understanding of the lessons of the Iraq War, the Libya intervention, and, yes, US mistakes during the Cold War. "The point about foreign policy is not just to know that you can overthrow a terrible dictator; it's to understand what happens the day after."

That's not a foreign policy, and Sanders didn't try to pretend that it was. He didn't try to argue that he has a superior plan for, say, Syrian peace talks, because he doesn't seem to have a plan at all. So rather than continuing to fight that losing battle, he is trying to present his judgment as the counterbalance to Clinton's expertise.

Clinton did not seem to have a good answer for this. She tried to challenge Sanders on judgment by accusing him of supporting the Libya intervention he now opposes, and of calling for Iranian troops in Syria. Neither is true, and both fell flat: Sanders co-sponsored a largely symbolic resolution calling for democratic change in Libya, and he never called for Iranian troops in Syria.

So Sanders could at least justifiably argue that their exchange on foreign policy could be considered a tie, that his judgment matches her expertise. That's a pretty big improvement for him.

Clinton's record does suggest that she has foreign policy principles: her wariness of regime change in Egypt but support for it in Libya, her reset with Russia and outreach to Iran, her construction of international institutions in Asia to peacefully counter China. But she is not expressing those ideas. And so, much as Sanders had previously let Clinton dominate a foreign policy dispute that should always have been contested, now Clinton is letting Sanders dominate a question of foreign policy principle that should likewise be contested.

4) Neither candidate is really able to present a foreign policy worldview

For Clinton to return Sanders's challenge on judgment, she would need to do more than just scramble to defend the Libya intervention or make some unfair attacks against Sanders; she would need to present a broad vision for foreign policy that demonstrates both expertise and judgment.

She has done this in more limited ways and in more comfortable settings, such as a November speech on the Middle East at the Council on Foreign Relations, which did articulate broader guiding philosophies.

But we saw in this debate that she is not able to do that specifically against Sanders. That's a serious political weakness. But it also suggests a more significant weakness in Clinton's larger foreign policy worldview if she is so unready to present or defend it when that worldview comes under criticism.

Every time she was challenged, Clinton retreated into technocratic recitations of minutiae — showing her expertise, sure, but also seeming to demonstrate Sanders's point that her expertise is great but not a replacement for judgment.

Sanders was not much better. He argued repeatedly that he has superior judgment, but demonstrated this only by describing the past mistakes he opposes. The closest we got to an actual foreign policy was Sanders declaring that he is against regime change, war, and unintended consequences:

As president I will look very carefully about unintended consequences. I will do everything I can to make certain that the United States and our brave men and women in the military do not get bogged down in perpetual warfare in the Middle East.

Those are good lessons, but they're not really sufficient, on their own, for conducting US foreign policy. It's not enough to know what he won't do; we also need to know what he will do.

As Foreign Affairs editor Justin Vogt put it, "I liked Sanders' riff on unintended consequences. But I'm still unclear on his *intended* consequences when it comes to foreign policy."

5) There were only two policy disagreements — both echoes of the 2008 Democratic primary

If you look past the arguments over Henry Kissinger or abstract questions of judgment, you see just two real differences over actual policy. Both, oddly, are near-exact repeats of Clinton's disagreements with Obama in 2008 — but much fainter this time around.

The first is regime change: Sanders opposes it, and Clinton, while she's not exactly making passionate stump speeches in favor of it, has certainly supported it in the past. In this, Sanders is hoping to repeat Obama's highly effective 2008 attacks on Clinton for supporting the Iraq invasion, a criticism he is extending also to Libya.

This will certainly resonate with Sanders's base on the left, particularly given that he is offering them so few actual foreign policy ideas. But it's not clear that Clinton supporters are going to be shocked to learn she voted in favor of the Iraq War in 2002 and thus reconsider her. Nor is it clear that voters as outraged over the Libya intervention today as they were over Iraq in 2008.

The second dispute is over diplomacy with Iran, which in 2008 Obama supported — to great controversy — and Clinton strenuously opposed.

Sanders is again hoping to resurface this debate and thus position himself as embodying Obama's ideals of diplomacy over war. And Clinton, unwisely, has indulged him, positioning herself as the tougher candidate on Iran.

This argument is kind of ridiculous. In 2008, there was real substance to the disagreement. Today there is not.

First of all, Sanders can't really credibly argue that Clinton is hostile to diplomacy with Iran, given that her State Department launched the most significant opening with Tehran since the 1979 Iranian Revolution.

Nor can Clinton honestly accuse Sanders of being dangerously soft on Iran, as she has tried to do, both because she herself conducted diplomacy with Tehran and because her attack line is patently false.

6) Bernie Sanders has a (relatively minor) Winston Churchill problem

When Sanders was asked to name a foreign leader that he admires, his answer was former British Prime Minister Winston Churchill:

In the same light, as the foreign leader, Winston Churchill's politics were not my politics. He was kind of a conservative guy in many respects. But nobody can deny that as a wartime leader, he rallied the British people when they stood virtually alone against the Nazi juggernaut and rallied them and eventually won an extraordinary victory. Those are two leaders that I admire very much.

Churchill is best remembered in the United States for his role in World War II, but he is remembered in much of the world as a brutal imperialist who championed the worst of European colonialism's racism and violence.

It's not just that Churchill made racist comments at a time when overt racism was more common; as the Washington Post's Ishaan Tharoor has written, "He presided over the hideous 1943 famine in Bengal, where some 3 million Indians perished." His other crimes in India include deliberately fostering sectarianism — a classic British tool of divide and rule — that cost lives at the time and still troubles the subcontinent today.

It was a bit ironic, then, that Sanders unmasked Henry Kissinger as an unduly celebrated war criminal, then turned around and praised a different unduly celebrated war criminal.

Obviously, Clinton's Kissinger moment was substantially far worse given that Clinton has personally spoken to Kissinger, whose crimes came during her lifetime. There is valid concern, particularly but not only on the left, that Clinton would be too willing to repeat Kissinger-style policies of militarism or regime change, whereas I don't think people seriously fear that Bernie Sanders is going to recolonize the Indian subcontinent.

Still, the dissonance between Sanders's moral superiority on Kissinger and his willing embrace of a brutal colonial overlord speaks to the gap between his embrace of symbolic principle — a good thing, to be sure, and a strength for him — versus his much weaker engagement with the actual substance of history or policy.

It's great that Sanders has chosen principle over the establishment when it comes to Kissinger, but the fact that he didn't see this same dynamic in the establishment's love of Winston Churchill helps to show, in a small way, why nearly all foreign policy experts worry about him.

Principle is only so useful when you don't have the knowledge to guide you in applying those principles. And there is real reason, going far beyond the Churchill moment, to worry that Sanders does not have that knowledge.