President Donald Trump's views on foreign policy -- and, really, everything -- are surprisingly simple: He likes people who are nice to him and do things he wants and he doesn't like people who aren't nice to him and don't do things he wants.
So, his views on any given issue or foreign leader are largely informed by how that person has treated Trump in their last interaction -- and how much of what he wants that they are willing to give him.
That worldview is important to keep in mind as Trump travels to Canada to attend the G7 summit on Friday, a trip which he has already tried to wiggle out of, is cutting a day short and, if Twitter is any indication, is assuming will be a total and complete disaster.
"The European Union treats us very unfairly," Trump said as he left the White House Friday morning to head to the G7. "Canada [treats us] very unfairly."
That's the latest in a series of increasingly frustrated and angry comments coming out of the White House over the past few days, as its become more and more clear that leaders Trump thought were his friends -- French President Emmanuel Macron and Canadian Prime Minister Justin Trudeau -- have pushed back on his demands, particularly on tariffs.
Trudeau and Trump had a reportedly contentious phone call late last month as the Canadian leader expressed his unhappiness with the United States imposing tariffs on its neighbor to the north for "national security reasons."
And Trump has repeatedly antagonized Trudeau in the run-up to the G7 meeting.
"Prime Minister Trudeau is being so indignant, bringing up the relationship that the U.S. and Canada had over the many years and all sorts of other things...but he doesn't bring up the fact that they charge us up to 300% on dairy - hurting our Farmers, killing our Agriculture!" Trump tweeted Thursday night.
He kept up that drumbeat Friday morning, tweeting: "Canada charges the U.S. a 270% tariff on Dairy Products! They didn't tell you that, did they? Not fair to our farmers!" (It's slightly more complicated than that.)
Even Macron, the world leader with whom Trump appeared to have the warmest relations, has come under fire from the President's Twitter account.
"Please tell Prime Minister Trudeau and President Macron that they are charging the U.S. massive tariffs and create non-monetary barriers," Trump tweeted. "The EU trade surplus with the U.S. is $151 Billion, and Canada keeps our farmers and others out. Look forward to seeing them tomorrow."
That tweet came after -- stop me if you've heard this one! -- a heated phone call between Trump and Macron earlier in the week in which the French President expressed his unhappiness with Trump's policies on immigration and trade.
Trump expected more capitulation from the likes of Trudeau and Macron because, well, they had been nice to him. They had, of course, done that out of a (mistaken) belief that praising Trump and playing to his desire to be venerated would make him more malleable to their policy wishes.
"Even as late as Thursday afternoon, Trump was questioning why he would attend a G7 meeting where he's outnumbered on key issues like trade and climate change. As a series of combative tweets from Macron began emerging late in the day, Trump again raised the prospect of scrubbing all or part of his visit to Canada, asking advisers what the point of attending the summit would be, according to a person familiar with the conversations."
This my-way-or-the-highway (or take-my-ball-and-go-home) approach is what Trump promised as a candidate for president. Past holders of the office had made terrible deals for the US -- Trump would make good ones. He alone knew how to talk to world leaders to get them to do exactly what he wanted. It was all in the art of the deal.
Campaigning is easy. Governing is hard.
And it turns out that simply telling other countries to, say, pay for a border wall (and enjoy it!) or renegotiate broad and complex trade deals isn't as easy as firing someone on a reality TV show.
That reality makes Trump mad. And when he gets angry, he tweets. Watch his Twitter feed over the next 24-48 hours.