BRUSSELS — The rest of the world has been wondering whether President Donald Trump is truly intent on continuing to rattle relationships with long-standing allies while drawing America closer to Russia. This week, they'll get perhaps the best indication yet of his intentions.

Trump arrived here today for the first leg of a weeklong trip in which he plans to ramp up pressure on other North Atlantic Treaty Organization countries to take more responsibility for their collective defense, sit down with both Queen Elizabeth II and Prime Minister Theresa May in England amid "Brexit"-fueled chaos in May's government, and meet privately with Russian President Vladimir Putin in Helsinki.

He does so in an environment defined by his foreign policy choices to date: the rising self-created tension between the U.S. and its European partners over tit-for-tat tariffs, his increasingly laissez-faire approach toward Russia's projection of physical and cyber power, and his explicit and implicit threats to diminish America's role in an alliance built to protect the rest of Europe from Moscow if partner nations don't pony up more cash.

This trip gives Trump the chance to tilt back toward most of Europe, or inch closer to Russia.

Shortly before departing Washington, Trump hinted that he intends to stick his fingers in the eyes of NATO, tweeting "NATO countries must pay MORE, the United States must pay LESS. Very Unfair!"

Asked later whether Putin is a friend or foe, he replied, "I really can't say right now. As far as I'm concerned, a competitor."

Still, Trump administration officials insist that the president's aims are to strengthen NATO by extracting more concessions from American allies, and to deliver a stern message to Putin about Russia's meddling in U.S. elections — even as his own rhetoric and actions suggest the former claim is in question, and he doesn't believe the latter is true.

"The major thing, the major deliverable, the major overall theme of this summit is going to be NATO's strength and unity," Kay Bailey Hutchison, the U.S. ambassador to NATO, said. "I would say our major areas of deterrence would be Russia and the malign activities of Russia, the efforts of Russia to divide our democratic nation, [Intermediate-Range Nuclear Forces] Treaty violations. All of those things are now being addressed by NATO in a strengthened deterrence and defense."

There's broad agreement about those goals in European and domestic establishment foreign policy circles, but deep concern that Trump could flip the equation on its head and provide an opportunity for Putin to gain strength vis-a-vis NATO countries.

"What we want is a sense of unity. That sounds like a very base, low standard, especially with him going on to meet Putin," said Laura Rosenberger, director of the German Marshall Fund's Alliance for Securing Democracy and a foreign policy adviser to Hillary Clinton's 2016 presidential campaign.

"Anything that does not seem to show a unified front is one that a) is going to leave allies nervous and b) is going to give Putin a sense that he has space to exploit and he will, of course," she said. "Even without some big crack showing up in Brussels, Putin surely see lots of places that he can play Trump and exploit tensions in the alliance."

'We're the schmucks that are paying for it all'

At a re-election rally in Great Falls, Montana, last week, Trump complained about the U.S. trade deficit with the European Union, which stands at about $150 billion annually, and the reluctance of some countries to meet a 12-year-old agreement that each nation would contribute at least 2 percent of its gross domestic product to its own defense.

His argument is that the U.S. is getting taken for a ride by European trading partners that rely on American money to defend them from Russia and other threats. He singled out Germany, which imports oil and gas from Russia, while spending far less than 2 percent of its GDP on defense.

"We're the schmucks paying for it all," he told the audience, adding that he has said to German Chancellor Angela Merkel he doesn't believe the U.S. gets as much out of NATO's mutual-defense pact as Germany does.

One fear in Europe — and among those in Washington's foreign-policy establishment — is that Trump might eventually follow through on his threat to withdraw U.S. forces from Germany, where more than 30,000 American troops are stationed, and diminish that deterrent to Russian aggression.

That may help explain why Germany is expected to announce this week that it will increase the share of its GDP devoted to defense from 1.2 percent to 1.5 percent by 2025.

More broadly, Trump has shown deep disdain for NATO from his days on the campaign trail.

"I think NATO's obsolete," he said in 2016. "NATO was done at a time you had the Soviet Union, which was obviously larger, much larger than Russia is today. I'm not saying Russia's not a threat. But we have other threats."

While he has since rescinded his oft-articulated analysis that the alliance is "obsolete," Trump said in Montana last week that "NATO is killing us."

But Trump's last-minute decision to pull out of a joint statement with other G-7 countries after a summit in Canada last month has heightened worries that he will pull a similar move at the end of NATO's meeting.

The 'Special Relationship'

On Thursday, Trump will make the 200-mile hop from Brussels to London, where he'll show up in the midst of a crisis over May's handling of Britain's exit — or "Brexit" — from the European Union.

During his short stay, he is expected to be met, separately, by May and Queen Elizabeth — as well as a gigantic inflatable "Trump Baby" balloon with a blond coif, small hands and a white diaper that has become the symbol of the significant protests expected to greet him in the United Kingdom.

A helium-filled Donald Trump blimp which will fly over London during his visit is inflated. Simon Dawson / Reuters

The two big questions on the U.S. side are whether Trump will make progress toward a bilateral trade deal with the U.K., and whether he will involve himself in the debate over May's proposal for a softer detachment from continental Europe than many of her conservative allies would like.

Boris Johnson, her foreign minister and the face of the Brexit movement, resigned from May's Cabinet Monday following the weekend departure of David Davis, the official responsible for the Brexit process, and there is a real chance the conservative caucus could vote to oust her soon.

There's a "big push on" to sack May, said a U.S. source with ties to British conservatives. "Trump visit couldn't come at a worse time for May."

So the big question for May is whether she will survive politically, with key figures in her own party abandoning her government in protest of a Brexit plan that would keep the U.K. in line with the parts of the European Union's "common rulebook" that deal with trade in goods.

"The Tory Brexit plan that took two years to develop has unraveled in two days," said Matthew Doyle, who served as political adviser to former Prime Minister Tony Blair. If May backs away from the so-called Chequers plan quickly, the damage will be "serious but not automatically fatal," Doyle said.

President Donald Trump greets British Prime Minister Theresa May in Washington on Jan. 27, 2017. May was the first foreign head of state to meet with President Trump at the White House. Shawn Thew / EPA

Still, it would be understandable if May is a little distracted Thursday evening, when she is scheduled to host a black-tie dinner for Trump at Blenheim Palace, the birthplace of Winston Churchill, and during their business meetings Friday.

Trump said Tuesday that May's future is "up to the people" — though it may really be determined by her own fellow party members.

While Trump applauded British voters for "taking their country back" when they opted for "Brexit" in 2016, he isn't advocating either a hard or soft detachment from the continental economic alliance, U.S. Ambassador to the U.K. Robert "Woody" Johnson said. And yet it would hardly be surprising if Trump weighed in again on the future of the nationalist plebiscite that many international political observers believe presaged his 2016 victory, particularly given his starchy relationship with May.

The British are eager to get Trump to take a tougher line with Putin, particularly with regard to the poisoning of a former Russian spy and his daughter on British soil in March. Last week, two British citizens became ill from exposure to the same nerve agent, Novichok, at a nearby location — with one of them dying over the weekend.

"The eyes of the world are currently on Russia,” British Home Secretary Sajid Javid said. “It is now time that the Russian state comes forward and explain what has gone on."

Russia has denied involvement in the poisonings, and argued that Britain is preventing a joint probe.

It remains to be seen whether Trump, who has split with administration officials and members of Congress over their conclusions that Russia meddled in his 2016 election, will press Britain's case with Putin. And there are concerns that he isn't ready to represent the interests of America and its allies in Helsinki.

Following a meeting with Queen Elizabeth at Windsor Castle Friday — where etiquette reigns supreme — Trump plans to spend the weekend in Scotland.

The Finnish Line

After returning from an all-Republican congressional trip to Russia last week, Sen. John Thune, R-S.D., said lawmakers took a hard line with Kremlin officials on a variety of subjects that could come up when Trump sits down with Putin on Monday.

"During our meetings, we stated in no uncertain terms that Russia must stop its meddling in our elections and that its destabilizing actions in the region are not without consequence," Thune said. "The delegation also stressed that Russia respect the sovereignty of Ukraine and help bring about a peaceful resolution in Syria. These discussions were direct and to-the-point. It’s now up to the Russian government to demonstrate that it will be a responsible actor on the world stage.”

But Trump's relations with Russia have been complicated by his domestic politics. He has often questioned whether Russia interfered in the 2016 election as part of his defense against a special counsel investigation into possible collusion between his campaign and Moscow and allegations that he has obstructed justice.

And, specifically, he has said he takes Putin at his word that Russia wasn't involved — a position at odds with the assessments of the Obama administration, his own national security officials and a bipartisan Senate investigation into Russia's role in influencing U.S. elections.

"Every time he sees me, he says, 'I didn't do that,'" Trump said last November. "And I believe, I really believe, that when he tells me that, he means it."

To deter Putin, Trump would likely need to draw a very clear line — one far tougher than any of his public statements to date.

"The lack of any clear message," Rosenberger said, "will be taken by Putin as license to continue in particular in the run-up to 2018 and beyond."

CORRECTION (July 10, 2018, 2:30 p.m. ET): An earlier version of this article misstated the effect of the poisoning attack on a former Russian spy and his daughter. The two survived the attack; they did not die. The article also misstated when they were poisoned. It was in March of this year, not March 2017.

An earlier version of this story also misspelled the first name of the U.K. prime minister: She is Theresa May, not Teresa May.