A good Anglophile knows that an audience with Queen Elizabeth II is planned well in advance: from the way a guest greets her — bow or curtsy — to the way she is addressed: “Your majesty” first, “ma’am” thereafter.

In the court of Emperor Trump — as the Sun's political editor Tom Newton Dunn dubbed the White House on Thursday — nothing is certain. Britain and its prime minister have learned this lesson the hard way.

Prime Minister Theresa May already faced an arguably impossible task ahead of the president's visit: Impress Trump and shore up a trade deal without appearing too deferential before a disapproving public.

A YouGov poll revealed only half of Britons felt Trump’s visit should have gone ahead, and the majority of the British population think he is a racist. Yet supporters of Brexit see a U.S. trade deal as a central plank of their strategy: Vote Leave, the campaign to leave the European Union, said post-Brexit trade deals centering on the United States could create 284,000 jobs.

10 Downing Street resolved this tension by planning a swift “business visit” that would avoid protests or any population centers. It also urged Trump’s team to avoid meetings that could lead to a breach of protocol and undermine talks, such as appearing on Nigel Farage’s shock-jock radio show.

The Sun interview that appeared late Monday exceeded the prime minister’s worst nightmares. The president stunned Britain by declaring there would “probably” be no free trade deal with Britain if Theresa May adopted her current Brexit strategy. The tabloid concluded: “US deal is off!”

Jacob Rees-Mogg — an member of Parliament whose aristocratic drawl and rich historical references have earned him the nickname “the Honorable Member for the 18th Century” — has led the opposition to May's post-Brexit blueprint, and is a favorite to succeed her. He pounced on the remarks, saying Friday morning that Trump’s interview proved he understood the flaws of her plan more than government ministers.

Within hours, however, Trump had flip-flopped and denied criticizing the prime minister, insisting: “We want to trade with the U.K., and the U.K. wants to trade with us.” He even said she was an “incredible woman” doing a “great job.” Such hyperbole is rarely reserved for the British prime minister, whose aloofness and unpopularity led to her party losing a parliamentary majority in the most recent general election. This week her approval ratings reached an all-time low — with only 25 percent in favor.

The reality is that no one knows which position to take more seriously — the Sun interview or Trump's U-turn — and the president may not know himself.

He has made clear he wants Brexit to succeed, both as a lifelong Euroskeptic and a person who predicted his own populist victory would be “Brexit plus plus plus.” Former president Barack Obama said a vote to leave the bloc would put Britain “at the back of the queue,” so signing a trade deal, further undermining his predecessor, has a special allure.

At the same time, the president may also be sincere in his belief that May’s blueprint leaves Britain too closely entangled with the E.U. to make a trade deal with the United States palatable or even possible. “We have enough difficulty with the European Union,” he said Thursday.

Nor is his opposition to May's strategy without precedent: In less publicized remarks made late last year, Commerce Secretary Wilbur Ross warned Britain on Trump's behalf that it must strike a deal with Europe that “takes into account our commercial interests and does not hinder the development of a closer post-Brexit U.S.-U.K. relationship.”

This illustrates how a trade deal with May's Britain would bring into conflict two of Trump's core convictions: that Brexit is essentially good and that dealing with multilateral treaties or institutions, whether NAFTA or the E.U., is bad. As Britain's departure from the bloc draws nearer, Downing Street will hope Trump is willing to compromise and put his faith in May's Brexit.

The fact remains that Trump is one of a handful of world leaders who has expressed a belief in Brexit, and he could yet provide a trade deal as talks with the E.U. founder. But Britain has today learned that its future is built on the whims of a world leader who is perhaps more mercurial than any other.