It can be hard to see a clear picture of U.S President Donald Trump's foreign policy, especially in a week like this one.

Last weekend, following his appearance at the G7 summit, Trump directed angry tweets about trade at Prime Minister Justin Trudeau.

On Tuesday, Trump shook hands with North Korea's leader Kim Jong-un and promised total denuclearization despite the lack of a clear roadmap.

Then, on Friday, Trump slapped $50 billion worth of tariffs on Chinese exports.

While his approach may seem opportunistic, Thomas Wright, a senior fellow with the Brookings Institution, says that Trump's worldview is largely unchanged from perspectives he held in the '80s.

Wright wrote about Trump's long-standing approach to foreign diplomacy for Politico and revisited some of the president's past comments on trade and world leaders with Day 6 host Brent Bambury.

Here's part of their conversation:

Brent Bambury: Jeffrey Goldberg reported this week in The Atlantic that a senior White House official told him Trump's doctrine is summed up with three words: 'We're America, bitch.' Does that sound right to you?

Thomas Wright: It's a little crude, but I think it does reveal something about the mindset of the administration of the president. And in Jeff's piece he said that he heard three different comments from White House officials.

One was, 'We're America, bitch.' The other was, 'No friends. No enemies.' And the third was, 'Permanent destabilization is good for America.' And I think all of those things describe elements of President Trump's worldview.

Canada's Prime Minister Justin Trudeau shakes hands with U.S. President Donald Trump during a meeting at the G7 leaders summit in La Malbaie, Que., on Friday, June 8, 2018. (Justin Tang/Canadian Press)

BB: And you anticipated this worldview, this doctrine. In 2016 more than a year before he became president, you wrote about what could become Trump's foreign policy. How did you go about determining what his foreign policy doctrine would be at that early stage?

TW: It turned out, when I started to look into it, that there were a lot of signs and evidence there if one looked. And so Trump had been talking about — even obsessing about — America's role in the world since 1987.

1987 is the first year we can find where he really begins to talk at length, and the things he talked about then are very similar to what he talks about now.

So what I found was that he doesn't like America's alliances. He's very critical of allies. He doesn't like free trade. He's constantly proposing protectionist measures. And he likes authoritarian leaders, especially of the Russian variety. And those three things he's really been remarkably consistent on, and I think they continue to drive policy today.

BB: The Cold War was still on in 1987. How did he show some sympathy toward Russian leaders when America was in an existential battle with the Soviet Union?

TW: The Russia comments come a little bit later, in 1990, at the time when Gorbachev's rising to power. He visits Moscow, and he comes back and he says that he doesn't like Gorbachev because he's not a strong Soviet leader and he should have behaved like the Chinese did in Tiananmen Square. That he should have put down the revolution in the same way that the Chinese Communist Party did.

So it's not that he takes Russia's side in the Cold War, it's really that he's angry at America's allies and then he is supportive of an authoritarian rule in Russia after Gorbachev comes to power.

He's the proverbial broken clock that's right twice a day. - Thomas Wright, senior fellow with the Brookings Institution

BB: But a lot of people were caught off guard by Trump's behaviour towards his allies at the G7 summit last weekend. I take it you were not surprised. Do you think that people should have known better than to think that there would be harmony coming out of that meeting?

TW: The thing with Trump is he's always shocking, but I think he's not all that surprising, in that he does things that shock the senses, that are outrageous. But I do not think it was a surprise that he clashed with U.S. allies at the G7.

In fact I think what would have been surprising is if it went very well and he reaffirmed the importance of the Western alliance and talked about shared values and history, because that's something he's never ever done.

You know he wants to impose tariffs. He wants to criticize allies. He wants to reach out to Russia, to other authoritarian leaders. And that's exactly what we're seeing in 2018.

Germany's Chancellor Angela Merkel, U.S. President Donald Trump, Prime Minister Justin Trudeau and France's President Emmanuel Macron chat during a family photo at the G7 Summit in the Charlevoix city of La Malbaie, Quebec, June 8, 2018. (Yves Herman/Reuters)

BB: So he believes that, as you said, the global economy has been unfair to the United States. It would seem that there are many Americans that agree with him on that. Do you think that he can make a cogent argument for why he's right on it?

TW: A cogent argument? No, because he's the proverbial broken clock that's right twice a day. You know, he's been making this argument since the mid-'80s and it hasn't changed. It's just that it resonates a little bit more now.

But he finds it very hard to articulate the case. I mean, his basic understanding of the global economy is on trade deficits in particular sectors.

He doesn't pay any attention to services. He can't really explain why trade deficits are bad. He doesn't have any understanding that the U.S. is the consumer of last resort and that's connected to the role of the dollar. There's no sort of understanding, I think, of how all of this knits together.

So his view is that the U.S. ought to be in surplus with every country in the world in manufacturing. And that is, you know, a fantasy.

This interview has been edited for length and clarity. To hear more from Tom Wright, download our podcast or click 'Listen' above.