After a warm welcome in the Middle East and a "fantastic" visit with the pope, U.S. President Donald Trump walks on shakier ground on Thursday when European Union and NATO leaders will press him on defense, trade, and environmental concerns.
The Republican president, midway through his first foreign trip since taking office, has basked in the glow of favorable receptions in Riyadh and Jerusalem, where leaders lauded his harsh words for Iran.
Praise may be in shorter supply in Brussels.
Trump questioned the relevance of the NATO military alliance as a presidential candidate, and is considering pulling the United States out of the Paris agreement on climate change - a huge concern in Europe. The EU was also a party to the Iran nuclear agreement, which Trump has criticized sharply.
"We expect him to recommit to NATO's founding rule that an attack against one ally is an attack against all," said a senior European diplomat at the North Atlantic Treaty Organization.
"Words matter and there is a huge expectation on that."
Trump will also meet Europe's chief executive Jean-Claude Juncker and European Council President Donald Tusk, who chairs EU summits, in the morning.
He will then go to NATO's new, billion-dollar headquarters where he will unveil a memorial to the Sept. 11, 2001, attacks on New York and Washington.
There Trump, in his only scheduled public remarks before a dinner with NATO leaders, is expected to pledge his full support to the alliance he once called "obsolete" because he said it was not doing enough to stop terrorism.
NATO hopes to impress Trump with military bands, allied jets flying overhead and a walk through the glass-and-steel headquarters, which replaces a leaking, 1960s prefab structure.
U.S. Secretary of State Rex Tillerson said Trump would press NATO leaders hard to spend more on defense and take on more of the burden of paying for the alliance, a message Trump has reiterated repeatedly before and after entering the White House.
Trump wants NATO to join the battle against Islamic State, Tillerson told reporters on Air Force One.
NATO ambassadors agreed on Wednesday for the Western military alliance to join the U.S.-led, 68-nation coalition against Islamic State in Syria and Iraq, paving the way for a formal endorsement by NATO leaders.
EU "WONDERFUL" OR NOT?
There may be tension at the EU meeting, too, given the U.S. president's earlier apparent disdain for the bloc. In January, Trump labeled the European Union a "vehicle for Germany", called Britain's decision to leave the bloc a "great thing" and said more countries would follow.
But EU officials were pleased he was fitting in the visit at all and noted that his critical tone had changed after meeting with German Chancellor Angela Merkel in Washington and after sending U.S. Vice President Mike Pence to Europe this year.
Trump told Reuters in February the EU was "wonderful".
"We saw two different Trumps," one EU official said, describing campaign comments about the benefits of Britain's exit and probability of further departures as "the Nigel Farage era" when the UK Independence Party leader had Trump's ear, and saying that was followed by a "more pragmatic and realistic" approach once Trump was installed in the White House.
EU leaders may be looking for hints from Trump about the U.S. trade relationship after the president kicked off plans to renegotiate the NAFTA agreement with Canada and Mexico.
U.S.-EU trade represents about 46 percent of the global economy, said Jeffrey Rathke, a Europe expert at the Washington-based Center for Strategic & International Studies, but negotiations on a broad EU-U.S. free-trade agreement have been on hold since Trump's predecessor Barack Obama left office.
"The administration has not yet articulated any kind of agenda for the (trade) relationship with the European Union," Rathke said.
"This is a big, glaring hole ...This meeting may be an opportunity to start setting some direction on that," he told reporters ahead of the trip.
(Additional reporting by Robin Emmott and Alastair Macdonald; editing by John Stonestreet)