Trump faced protests on his arrival in Brussels, but he is getting a red-carpet welcome from Western allies eager.
Trump faced protests on his arrival in Brussels, but he is getting a red-carpet welcome from Western allies eager to persuade him that his earlier criticisms of them were misplaced.
NATO, which Trump on the campaign trail dismissed as "obsolete" for focusing on Russia instead of terrorism, is set to bow to his demands that it join the US-led coalition against the Islamic State.
"This will send a strong political message of NATO's commitment to the fight against terrorism," NATO Secretary General Jens Stoltenberg told a press conference ahead of the summit.
Trump's entourage however warned that the billionaire president will once again press the 28-nation alliance to pay their full share of the alliance's financial burden.
"I think you can expect the president to be very tough on them," Secretary of State Rex Tillerson told reporters travelling with Trump.
Trump himself however is set to face pressure from British Prime Minister Theresa May over leaks to the US media of details of the probe into the bombing of a pop concert Monday in Manchester that killed 22 people.
Brussels could be the toughest leg yet of what has so far been a largely trouble-free first foreign trip for Trump, who came direct from a meeting with Pope Francis at the Vatican.
On his arrival on Wednesday in Brussels, the city he once said had been turned into a "hellhole" by Muslim immigration, the president was greeted by thousands of protesters saying "Trump not welcome."
Further protests were expected Thursday and security was tight across the city with helicopters flying overhead and key roads shut down.
The European Union, like NATO credited with keeping the peace in Europe since World War II, will also be hoping to convince Trump that it remains relevant.
EU President Donald Tusk, who will meet Trump along with European Commission chief Jean-Claude Juncker, tweeted that "I'll aim to convince POTUS that euro-atlanticism means the free world co-operating to prevent (a) post-West world order".
Trump alarmed the EU by backing further countries to follow Britain's lead in quitting the bloc, and by calling it a vehicle for German dominance of the continent.
Tusk and Juncker will tell the US president that since last year's shock Brexit vote, the EU is "in a completely different place" after populist candidates lost in France and the Netherlands, a senior EU official said.
Trump will have a private lunch with new French President Emmanuel Macron, whose recent victory over far-right leader Marine Le Pen has been seen as a beacon of hope by Brussels, before heading to NATO.
Trump set out his stall on terrorism as he met Belgian Prime Minister Charles Michel shortly after his arrival on Wednesday night, saying that the most important issue was terrorism after the "horrible situation" in Manchester.
"When you see something like what happened a few days ago you realise how important it is to win this fight. And we will win this fight," said Trump.
At least 9,000 people marched through Brussels on Wednesday night waving blond-haired effigies of the reality TV star president.
The NATO summit will however be full of pomp and symbolism, with the keen-to-impress alliance showing off its new $1.2-billion (1.1 billion-euro) headquarters and staging a flypast.
At a ceremony with German Chancellor Angela Merkel, Trump will unveil a memorial to the September 11, 2001 attacks featuring part of the destroyed World Trade Center, while Merkel does the same for a fragment of the Berlin Wall.
In return, allies rattled by a resurgent Russia will hope for a public display of commitment from Trump to Article 5, the alliance's one-for-all collective defence pledge.
While this has been triggered only once, by the US after 9/11, Trump has said that any future use might depend on whether a NATO member had met its spending commitments.
The alliance is now set to formally join the anti-IS coalition after France, Germany and Italy dropped their opposition, diplomatic sources said.
But while it will provide help including the use of AWACS surveillance aircraft it will not join combat operations, Stoltenberg insisted.
Trump's wife Melania, meanwhile, is set to visit a museum dedicated to the surrealist artist Rene Magritte and a leading leather store while in Brussels.
Trump's sweep through Saudi Arabia, Israel and the Vatican, centres of three of the world's main religions, is being followed by Brussels and a trip to Italy for the G7 leaders summit on Friday.
The high-profile trip has diverted attention from Trump's domestic pressures amid the probe into alleged Russian ties with his campaign.