It started with Democratic presidential nominee Hillary Clinton. Then it was Speaker of the House Nancy Pelosi.

And it's since been extended to the Duchess of Sussex Meghan Markle, San Juan Mayor Carmen Yulin Cruz, and Senators Mazie Hirono, Kamala Harris and Elizabeth Warren.

Now, it's Mette Frederiksen, the Danish Prime Minister.

Her sin?

Explaining that the Arctic island of Greenland was not for sale — and that she found the notion that the US President wanted to buy it "absurd".

"Greenland is not for sale. Greenland is not Danish. Greenland belongs to Greenland," she said.

Remember the ubiquitous "nasty woman" banners and t-shirts at the Washington DC Women's March the day after Donald Trump's inauguration?

It all began when the President called Hillary Clinton "such a nasty woman" during the third presidential debate in 2016. It quickly became a feminist, anti-Trump rallying cry, but that hasn't stopped the President from using it over and over again to describe women who stand up to or criticise him.

In this case, he promptly cancelled an upcoming visit to close ally Denmark, and called the Prime Minister (that's right, you guessed it) "nasty".

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"I looked forward to going but I thought that the Prime Minister's statement that it was 'absurd' … that it was an absurd idea that was nasty," he said.

"I thought it was an inappropriate statement. All she had to do is say no, we wouldn't be interested. You don't talk to the United States that way, at least under me."

Back up a second: What's this about buying Greenland?

Over the weekend, an anonymous Trump ally told the press that the President had explored purchasing Greenland. But he was just joking.

You could argue it was a classic Trump administration distraction play.

In a (relatively) slow US news week, the Democratic 2020 contenders were getting a fair bit of attention.

The other circulating stories weren't helping the President either.

The economy could tank just before Americans go to the ballot box, and, after talks with the NRA, Mr Trump backed away from tightening gun background checks — legislation that 89 per cent of Americans favour.

Donald Trump had his heart set on Greenland, but the Danish Prime Minister said it was not for sale. ( AP: Linda Kastrup )

But you could also posit that the Greenland rumour was a classic "trial balloon" to gauge how the press, pundits and public would react.

Because, believe it or not folks, there are several reasons the US might actually want to buy Greenland:

1. Resources. The Arctic island is rich in oil and a prime spot for shipping lanes, and as global warming thaws its icy depths, those resources will be easier to get at. 2. Geopolitics. Russia, China and a host of other nations have been shoring up military resources in the region, foreshadowing a fight over its potential riches and strategic location. 3. Legacy. Greenland is a big piece of real estate (or at least it looks that way on the map, thanks to the Mercator projection). The President prides himself on being a property mogul. Hence, such an acquisition would be a "win" in Mr Trump's book.

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And remember, the Americans actually bought Alaska from the Russians in the 1860s, so there is precedent.

Although the Danish Prime Minister's take was "the time when you buy and sell other countries and populations is over. Let's leave it there."

Whatever the reason, the trial balloon was pretty much popped when the media got wind of the idea. The New York Times called it "a headline seemingly straight out of The Onion."

Even the President himself appeared to acknowledge the idea was pretty out there, tweeting an image of a gleaming Trump Tower looming over a quaint village.

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But in the end, the mockery was enough to put the president on edge. Ms Fredericksen sent him overboard.

Then things went from bad to worse for diplomacy

"I actually think we have responded very nicely from the Danish side," she said in response to the "nasty" comments.

"When you are close allies and good friends, like Denmark and the US are, there should also be room for disagreements along the way. I hope we can stop this discussion soon."

But Mr Trump wasn't ready to let it go.

Attracting renewed criticism for damaging years of diplomatic doctrine with his direct language and approach, he took to twitter to attack NATO, a grouping that includes Denmark.

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Oh, and all of this happened just days before the President travels to France (a NATO member) for the G7 summit.

Washington types who've been shaking their heads this week are now shaking in their boots about what might happen next (although, that's been the status quo around here for some time).

Secretary of State Mike Pompeo jumped on the phone to do some damage control. Because while it's safe to assume the world's leaders are used to Mr Trump's mercurial behaviour that doesn't mean they like it.

(That, of course, is all part of the strategic chaos theory that drives the President and the way he controls the narrative.)

Contradicting the President comes with perils

Just this week, the President thanked Wayne Allyn Root, an evangelical talk show host, who claimed Jewish Israelis love Mr Trump like he is "the King of Israel."

When it came to "dealing with China," he looked to the heavens and claimed he is "the chosen one".

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Often, world leaders worried about losing a powerful ally in the US appease the President rather than contradict him. They swallow their tongues.

But for Ms Fredericksen, going along with the President's ideas would've, at best, made Greenland look as weak as Mr Trump implied it was or, at worst, made it seem like Greenland really was for sale.

To be fair, Mr Trump has also referred to men as "nasty".

But in that sense, his use of the label doesn't follow the same pattern. He's even used it to express his admiration for a man's political savvy.

What's different is that when he applies "nasty" to women, it's always meant as a conversation-stopping put down. And it's always because they disagree with him.

Ms Fredericksen's response had nothing to do with her gender. And yet by recycling the "nasty" moniker Mr Trump went there, yet again.