Donald Trump first expressed skepticism about the North Atlantic Treaty Organization (NATO) in March.

He didn't bring it up on his own, mind you, but after going back and forth with his Washington Post interviewers, he eventually settled on his position: It must be renegotiated.

"NATO is costing us a fortune and, yes, we’re protecting Europe, but we're spending a lot of money," he said. "No. 1, I think the distribution of costs has to be changed. I think NATO as a concept is good, but it is not as good as it was when it first evolved."

This is Trump's prescription for most things. Something isn't great? Make a better deal. It's totally nebulous, but it also totally fits with his brand as a negotiator and businessman.

Three months later, though, renegotiating NATO has become a Trump rallying cry — and he's even threatening to pull out altogether. In an interview with the New York Times this week, he openly flirted with pulling out and telling the other member countries, "Congratulations, you will be defending yourself." Then, Trump on Thursday added a section on NATO to his speech accepting the Republican nomination — after it initially didn't have one.

"Recently I have said that NATO was obsolete, because it did not properly cover terror, and also, that many of the member countries were not paying their fair share. As usual, the United States has been picking up the cost," Trump said. "Shortly thereafter, it was announced that NATO will be setting up a new program in order to combat terrorism — a true step in the right direction."

But before Thursday, Trump had spent very little time talking proactively about NATO, and fact checks of his past comments suggested he didn't really know all that much about how it works.

Still, it fit neatly with the theme of his speech Thursday night, which can be summed up in three words: "Americanism, not globalism."

"The most important difference between our plan and that of our opponent is that our plan will put America first," Trump said. "Americanism, not globalism, will be our credo."

So there it is: Trump himself saying this will be the key distinction of the 2016 general election. Populism is being rebranded as "Americanism, not globalism." The critics will call it nationalism.

The biggest expression of Trump's antipathy toward globalism, of course, is free trade deals. President Obama's Trans-Pacific Partnership (TPP) is bad, and NAFTA is a [Bill] Clinton-crafted disaster, he says. He has also criticized GOP-led foreign adventures, including the Iraq War. He even spoke favorably of the United Kingdom's decision to pull out of the European Union, also known as Brexit, last month.

Trump didn't go big on NATO in his speech Thursday — and indeed, his campaign sought to downplay his threat to pull out this week after controversy erupted — but its inclusion shows precisely where Trump's general election campaign is headed: inward.

Trump's entire campaign, of course, has been focused inward in one way or another. But Thursday's speech brought it to a whole new level. Trump painted a picture of an almost dystopian United States that needed to be dealt with before anything else can be.

In the New York Times interview, he even suggested the United States shouldn't lecture other countries while it has its own messes to deal with.

"I don't know that we have a right to lecture," he said. "Just look about what’s happening with our country. How are we going to lecture when people are shooting our policemen in cold blood? How are we going to lecture when you see the riots and the horror going on in our own country?"

As we've written, Trump took plenty of liberties in painting this picture of doom and gloom — crime for instance, has been dropping for years, not rising. But his decision to try and paint it otherwise suggests he would very much like to foment the kind of anti-globalism that led to the Brexit vote in the U.K. and, according to polling on free trade deals, could play quite well in the United States.

If Trump is to pull an upset this year, that's probably what does it for him.