In a recent piece for Foreign Affairs you argue that the classical version of US foreign policy cannot be revived. The title reads: “This time it’s different – Why US foreign policy will never recover”. What exactly is different this time around?

A few things are different. In some ways, there's two things that have happened in the United States that will make it difficult to go back to liberal internationalism. The first is political polarisation. This has been a problem that has been brewing for 30 or 40 years. But it used to not affect foreign policy. Foreign policy was the last preserve of bipartisanship for quite some time.

In 2016, I ran a series of conferences about foreign policy during the campaign. And what was striking to me was the degree to which the campaign people, the foreign policy people, on both sides were friendly with each other. They disagreed but there was a shared trust there. Even since 2016, that's broken down to some extent. So foreign policy has become increasingly a plaything of domestic politics, which makes it hard to do it seriously.

Another element is that the presidents are coming from ever-more extreme wings of the parties. You can argue that George W. Bush was the most conservative president the US had had in history. And then Bush was replaced by Barack Obama, who was the most liberal president we’d had in history; who was replaced by Donal Trump, who is even more conservative than Bush. It’s a widening oscillation.

Because of polarisation, the checks on the president in terms of foreign policy have become weaker and weaker. Congress has, over time, ceded both the power to declare war and the power over trade negotiations to the president. 1942 was the last time Congress officially declared war. An ever-increasing amount of foreign policy is run out of the executive branch, without any congressional buy-in or congressional oversight. If you combine these two trends, it means that it’s entirely possible that Trump will lose in 2020 and be replaced by someone like Bernie Sanders or Joe Biden.

But will the next president not in all likelihood attempt to rebuild liberal internationalism?

Sure. But there's a problem with that. Imagine an American foreign policy in which Donald Trump will be replaced by Bernie Sanders, who will be replaced by Senator Tom Cotton, who will be replaced by Alexandria Ocasio-Cortez. And with all the foreign power invested in the presidency, you will see each successive president essentially cancel what the previous president has done, in much the same way that Trump has done it with Obama on the Iranian nuclear deal, on the Paris Agreement, on the opening to Cuba.

So you would argue even a change in the White House will only add to the corrosion and would just be another tremor shaking the house?

Exactly. Trying to do grand strategy requires the ability to credibly commit. And the United States has nearly lost all its ability to credibly commit. In the United States, there's something called the Mexico City Policy. Essentially, this means if a Democrat is in power in the presidency, US aid agencies can donate to multilateral agencies and NGOs that provide family planning, including abortion. When a Republican is elected president, they reverse this policy and a ban is instituted. That's only a small issue and it’s been going on since the Regan administration. My concern is that all of foreign policy is going to move in that direction.

It seems that similar processes of shifting power to the executive branch are taking place around the world… in Russia, in China, in Israel, in Turkey. What’s its systemic effect?

One of instability. What’s the likelihood if you reach an agreement with someone, that the agreement will be sustained even if there's a shock of some kind? How do you develop trust? To be fair to Trump, what he’s doing in foreign affairs is not illegal. It’s not illegal to withdraw from the Iranian nuclear deal or from Paris Climate Accords. But in some ways the norm that we’ve always had, that you don't exit agreements your country has signed, is being eroded. You're right, that's not just Trump, that's also Putin withdrawing from the ICC or African countries doing so as well, so this is not just a US phenomenon.

How can trust be safeguarded?

There are two ways that you could try to promote trust, one is international law. If you have legislators that are involved, you use international law to lock in agreements and make it difficult to exit them. The other one, which is the kind that Trump and others such as Putin pursue, is a personal bond between leaders. But that's not sustainable.

From a historical perspective, you could argue we are returning to the ultra-personalisation of politics: feudalism, the personal relations between monarchs.

Yes, there's a certain element of that, except now we’ve added this populist element, where either someone like Putin or Erdogan, even though their democratic bona fides are weak, somehow claim to be speaking for the people. And then, people like Trump who claim that they're representing the forgotten people. The problem is that none of this is sustainable unless these leaders are in power for decades, which is an outcome I don't think would be good for anyone. And even then, it’s about as stable as the Molotov–Von Ribbentrop Pact. When interests change, then those agreements will break down because they won't be ratified in law.

You've been a very outspoken critic of President Trump. One of your Trump threads became so popular that it was reported it apparently “broke Twitter”…But while you're being critical of the president, your criticism goes well beyond Trump.

Yes, Trump is as much a symptom as a cause of what’s going on. There were times when the foreign policy community reached a consensus that proved to be grievously wrong. Going back to Vietnam, and more recently with respect to the Iraq war and the 2008 financial crisis. Part of the reason why Trump won in 2016 is because he ran on the idea that we should not rely on foreign policy experts – because look at the messes they've gotten us into. He embraced the idea that an amateur businessman could, somehow, do a better job.

We’re speaking in Hamburg, where you're going to give a lecture at the GIGA Institute. The German foreign minister has suggested an alliance of multilateralists to step up and protect the international order. How realistic is this?

There are things that can be done and also things that need to be negotiated. In trade, for example, it’s interesting to see the EU sign trade agreements with Canada and with Japan. The fact that TPP went ahead, despite the US withdrawal, I think, frankly surprised the Trump administration.

Eventually, what this is going to generate pressure on the United States to start engaging in the multilateral trading system again, because you're now seeing US businesses being disadvantaged, in terms of dealing with Japan or Korea or, eventually, the European Union.

There are also some interesting questions about what should be done to revive the WTO. I think there are other areas, however, where Europe has a choice to make, and I don't think it’s quite ready to make it yet. There are two primary areas where the United States still is unparalleled in the world. One is in security; the other is finance. And we’re seeing that the US use of financial statecraft, in terms of the US military, isn’t going anywhere.

Is Europe willing to actually engage in those kinds of hard power measures? Europe has the capacity to do this, I would add, if you combine the European Union, it’s an economy roughly the size of the United States. But that would require a very different strategy and a very different kind of social compact among the EU states that doesn't exist now.

To be the devil’s advocate, aren't we, perhaps just overly critical? Wasn't it Obama who said don't do crazy shit?

Yes. Don't do stupid shit, yes.

Well, there's a long list of stupid shit that this president could have done, including invading Iran, that he hasn't done so far. Should we not give him some credit for that?

Come back to me on that next month, I was going to say... You're right, on the one hand the pleasant surprise is that we haven't had a nuclear war. And we haven't had a global economic collapse.

And, if I may add given you wrote a pretty cool book on matter: we also haven’t witnessed the zombie apocalypse.

Yes, no zombie apocalypse either. But that’s the thing: what people forget is that I was an optimist in that book. If you read it, what I actually said was that the zombie movies are far too pessimistic. They always underestimate human ingenuity. In an actual zombie outbreak we would be fine. Now, I'm much more pessimistic. You're right: in some ways, relative to my baseline expectations, things could be much worse. But on the other hand, first of all, Trump still has almost two years left in office, things could get much worse. We’re seeing the Trump administration ratcheting up pressure on Venezuela, on North Korea, and on Iran. Not to mention a potential serious escalation of the trade war with China. It’s also disturbing that’s it’s not obvious how much input Trump is actually giving.

Well, it does seem like experts play a role, only that it’s the wrong kind of experts.

Well, it’s certainly not mainstream experts. It’s people like John Bolton and Mike Pompeo. And, indeed, this is one of the dangers of having a president who’s not just unschooled in foreign affairs but is also too proud to admit that he’s unschooled in foreign affairs. Say what you will about Barack Obama or George W. Bush, none of them had a wealth of foreign policy experience before they got elected, but they were also cognisant of that fact, picked their advisors carefully and were also willing, at times, to go against them.

Trump knows so little that it actually emboldens his subordinates to do things because they know that he’s not going to check their work. And so, this is how Bolton can rachet up the pressure against Venezuela and try to attempt a coup, which clearly failed. Or how Pompeo can try to escalate tensions against Iran.

Ultimately, this diminishes the administration’s credibility because Trump might wind up realising that, wait, we could potentially be in a war, I didn't want this, what are we doing? Trump has simultaneously become more predictable and less credible, because he constantly issues these blustery threats, but doesn’t always follow through. In fact, most of the time, he doesn’t follow through. The danger of that is there might be a time where he actually does want to credibly threaten something, but no one believes the threat.

Isn’t that exactly what is happening now?

Yes, the trade war is an example of that. The Chinese thought he was going to back down. Similarly, with North Korea, I think part of the reason the Hanoi summit doesn’t work is that Kim Jong-un thought that, in the end, Trump wanted a deal more than he wanted a good deal.

Part of the reason Trump is frustrated is that he doesn’t understand why no one takes his threats seriously. And the reason no one takes his threats seriously is that he threatens too much.

This interview was conducted by Michael Bröning.