BRUSSELS -- The new headquarters of the North Atlantic Treaty Organization -- a massive, state-of-the-art facility that cost more than a billion euros to build -- was designed to help the military alliance step boldly into the future.

The building is not completely ready, but on Thursday it will nonetheless greet U.S. President Donald Trump for an ad hoc meeting where everyone hopes to hear where exactly the leader of NATO's most powerful presence stands on the alliance's very existence.

The symbolism is not lost on Allen Sens, a political science professor at the University of British Columbia whose research focuses on international conflict and security.

"For decades, NATO has really needed a better facility," said Sens.

"Now it gets one -- at the precise moment that the volatility ... begins to suggest that divergent views and interests are beginning to cause a serious strain in the unity and the consensus of the alliance."

There is no overstating the importance of the United States to NATO, even in a forum where all 28 member nations -- including Canada -- have a voice in building consensus around the table.

"The American contribution to NATO is so immense that it really does define what the alliance does," said Shuvaloy Majumdar, a Munk senior fellow at the Macdonald Laurier Institute.

That has always been the case; the U.S. has long called for more equitable burden-sharing when it comes to covering the cost of deterrence and collective defence. But America's oversized role seems to bother Trump more than it did his predecessors.

On the campaign trail, candidate Trump famously described NATO as "obsolete."

And while he did say last month that he had changed on his mind on that front after learning more about what NATO does, he has never explicitly endorsed Article 5 -- the self-defence clause that means an attack on one member generates a response by all.

There were no doubt sighs of relief among allies Wednesday when U.S. Secretary of State Rex Tillerson, travelling to Brussels with Trump, said that his country would, "of course," support Article 5.

Still, they will want to hear it directly from the president, who will reportedly address the issue while unveiling a memorial at the new headquarters commemorating the invocation of Article 5 following the 9/11 terrorist attacks.

Trump remains adamant that other NATO members increase their defence spending, which is where things could get uncomfortable for Prime Minister Justin Trudeau. Canada spends just over one per cent of its GDP on defence, half of NATO's target, putting the country among the bottom third of allies.

The Liberal government argues that its contribution is bigger than the numbers suggest.

The Liberals point to Canada's commitment to send 450 troops to head up a multinational mission in Latvia, as part of efforts to curb Russian aggression in the Baltics, as well as the leading role it played in the NATO-led mission in Afghanistan.

Defence Minister Harjit Sajjan, who is joining Trudeau in Brussels, has said Canadians will see the results of that review June 7, although a federal official said Canada would be giving "high-level briefings" to some NATO partners.

Trump is also pushing for NATO to play a bigger role in the fight against the violently radical group known as the Islamic State of Iraq and the Levant, or ISIL.

Terrorism, which was already going to be a major theme of the Brussels meeting, is likely to get even more attention following Monday's deadly attack on a crowded concert arena in Manchester.

NATO has already recognized the threat posed by ISIL, and many members and partners -- again including Canada -- are already part of the U.S-led coalition in Iraq and Syria in one way or another.

A Canadian government official said Wednesday said the NATO member states are expected to produce statements on two issues: burden-sharing and some broad language on how NATO members can better co-operate to counter terrorism, including through intelligence-gathering.

These are big questions and there are other long-term issues that are expected to come up in conversation, including what to do about Russia, particularly in relation to Ukraine, but the official said a substantive communique will be saved for next time.

This time, it's about reaffirming the importance of NATO to one of its core members.

UBC's Sens, however, is setting the bar even lower.

"I think (everyone is) just settling for not having a disaster."