NATO is holding its breath.

Senior officials who thought they had won Donald Trump over when he declared last month that the alliance was “no longer obsolete” are hoping no plates or silverware go flying at a dinner Thursday where the U.S. president, after helping to inaugurate the alliance’s new headquarters, plans to browbeat his colleagues yet again about their meager defense spending.

Trump, who is on his first foreign trip as president, has long demanded that members of the alliance step up their military spending. On the campaign trail, he famously branded the alliance as “obsolete,” saying it did not do enough to fight terrorism, and in his first meeting with German Chancellor Angela Merkel he declared that her country “owed vast sums,” irking her and suggesting to many in Brussels that he understood little about NATO finances.

NATO Secretary-General Jens Stoltenberg has worked diligently in recent months to appease Trump, including by promising during a meeting last month in Washington that allies not meeting NATO’s spending target of 2 percent of GDP would develop individual plans by the end of the year, showing how they will reach that goal by 2024.

Stoltenberg has also persuaded allies to make demonstrative efforts on Trump’s other demand: that NATO step up its role in fighting terrorism, though on Tuesday afternoon in the wake of a deadly bombing at a concert in Manchester, allies were still meeting to try to figure out what concrete steps could be taken. One idea is that NATO, as an alliance, would join the U.S.-led global coalition fighting the Islamic State — a largely symbolic gesture because most NATO countries are already taking part.

Stoltenberg’s efforts are designed to provide Trump two clear victories on his first visit to NATO headquarters in Brussels. But no one — not even top White House officials — can be sure the president will take yes for an answer, or if he will shred months of meticulous planning with a few moments of discourteous bluster. And even if Trump plays along, paying his bounty carries a risk: When and where will his demands end?

"We don’t want improvisation at the table. We want carefully considered, thought-through decisions which are confirmed by heads of state and government” — Senior NATO official

The fear at HQ is well-placed. Trump may have declared NATO “no longer obsolete,” but that doesn’t mean he’s not on the warpath. As he heads to Brussels, people in his administration say he’s “excited” to put the squeeze on countries he views as deadbeat, freeloading allies. White House aides say he is looking in particular to Germany, already bristling at his demands, to take on a leadership role.

“I don’t know anyone who knows exactly what Trump is going to say,” said a senior NATO official who has worked on numerous summits. “Usually NATO events are highly choreographed. The staffs and the ambassadors with the capitals watching prepare all the decisions beforehand.”

“These are security and defense issues, so we don’t want improvisation at the table,” he added. “We want carefully considered, thought-through decisions which are confirmed by heads of state and government.”

Sharing the burden

Improvisation, of course, has been something of a hallmark of Trump’s presidency.

“I don’t know what he’s going to say, and I don’t know what the reaction would be,” the senior NATO official said. “I think everybody expects him to push on burden-sharing because he’s still saying it, because the guy who is writing his speech is talking about it.”

And the anxiety is not confined to Brussels. “I know that in the U.S. administration, they are holding their breath as well,” the senior official said.

In many ways, Stoltenberg can only hope that he has sufficiently prepped the members of the alliance so they are neither surprised nor annoyed when they hear Trump personally hammer a message that has already been delivered to Brussels by Vice President Mike Pence, Defense Secretary James Mattis and Secretary of State Rex Tillerson,

But the antipathy doesn’t run one way. While all of the allies were happy to see Trump’s U-turn on NATO’s relevance last month, he is widely viewed in Europe as an overly impulsive leader who poses a risk of worldwide chaos with every 140-character Twitter outburst.

Allies willing to increase defense spending note that they promised to do so long before Trump came on the scene. For many, the suggestion that they are acting in response to his arm-twisting is politically toxic at home.

“All of the allies have signed a pledge in 2014 to increase defense spending,” said Tomáš Valášek, who stepped down in March after nearly four years as Slovakia’s ambassador to NATO. “The way Trump has framed the request, as debt owed to the United States, that has grated. That has not been well received in Europe.”

“To imply, as President Trump has done, that NATO hasn’t been doing enough for the United States, well that hurts,” said Valášek, who is now director of Carnegie Europe in Brussels. “Because most, if not all, allies have been involved in Afghanistan and all have lost lives, and all have spent significant amounts of money.”

“There is no doubt in Europe that European defense as such have been under-financed, but there is a way to go about making the point,” Valášek added. “And the way President Trump has gone about it, in my humble opinion, has backfired because some countries are defensive.”

Subtlety, however, does not seem to be Trump’s preferred mode of delivery. And there is little indication that he will tread gently when he meets his fellow leaders at the gleaming new NATO headquarters.

Until now, Stoltenberg’s success in easing Trump’s skepticism about NATO could be viewed as an object lesson for other world leaders in how to shift the volatile president’s thinking.

“This administration wants to be clear and consistent that we will not let up,” a National Security Council official told POLITICO, adding that the administration has been monitoring the individual military budget of each NATO ally.

White House officials said Trump intends to make clear that his newfound support for the alliance is hardly unconditional. And one aide said Trump’s prepared remarks for the summit include a pointed message: “For the good of the alliance, all members must share responsibility and share the burden.”

Trump has already privately badgered leaders of NATO countries, particularly Merkel, during White House visits and over the phone. Two aides said that Trump found Merkel’s response — that Germany has a long-term plan for raising spending — to be insufficient.

“The president does view Germany as one of the most important countries in NATO,” the National Security Council official said. “It’s a large country — it runs a big trade surplus and has a big budget.” The official added, “It’s well under its target. It’s not as if Germany can claim they don’t have the resources. It’s a rich country. He wants it to be a leader.”

That sort of pressure has already led to angry pushback from Berlin, with German Foreign Minister Sigmar Gabriel saying Trump had wrongly interpreted the 2014 pledge by NATO allies to spend at least 2 percent of GDP on defense, and by Defense Secretary Ursula von der Leyen, who rejected Trump’s accusations that Germany owed “vast sums.”

'No longer obsolete'

Until now, Stoltenberg’s success in easing Trump’s skepticism about NATO could be viewed as an object lesson for other world leaders in how to shift the volatile president’s thinking, and how to deal with a man whose word is not necessarily his bond, but potentially a momentary whim.

Trump’s about-face on NATO nonetheless ranks high among his many reversals and self-contradictions, which include an abandoned campaign promise to label China as a currency manipulator and an about-turn on whether Syrian strongman Bashar al-Assad should stay in power. (He now thinks he should go.)

Aides to Stoltenberg, who had worked for months to help prepare for a make-or-break meeting in the Oval Office last month, watched in amazement as Trump stood with their boss during a live news conference at the White House and declared: “I said it was obsolete; it’s no longer obsolete.”

Never mind that Trump claimed credit for single-handedly arm-twisting the alliance into fighting terrorism (something NATO has viewed as a core duty since at least September 11, 2001) or that Trump made clear he would continue to browbeat allies into upping their military spending (a commitment they had all made in 2014). The world’s most powerful military alliance knows how to play capture-the-flag, and, from their perspective, Trump had just rolled his up and handed it over.

“It was incredible, really just incredible,” said one adviser to Stoltenberg who watched the scene on TV.

So how did Stoltenberg, a soft-spoken, cool-headed former Norwegian prime minister, sweet-talk the president?

Perhaps most importantly, the secretary-general never once criticized the president in public, nor, by all accounts, did he ever portray Trump’s demands as unreasonable — even in private meetings with leaders deeply skeptical of the president. Instead, Stoltenberg repeatedly told Trump that he was right to push for increased military spending and assured him that allies shared his desire for NATO to take a more active role in fighting terrorism.

Stoltenberg also reached out early for help from surrogates who would have Trump’s attention and respect, particularly Mattis, who served for three years as NATO’s supreme allied commander for transformation. Pence, who served a dozen years in Congress, was also a natural ally, as was H.R. McMaster, a former commander in Afghanistan, who took over as national security adviser from Michael Flynn.

Positive comments about NATO from a parade of leaders visiting Washington — including U.K. Prime Minister Theresa May, Merkel, Canada’s Justin Trudeau and Denmark’s Lars Lokke Rasmussen — also helped.

At NATO headquarters on Thursday, officials are hoping Trump’s remarks will be widely expected and sufficiently general so as not to upend the carefully orchestrated proceedings, which will include the unveiling of two memorials: a steel I-beam from the destroyed World Trade Center in New York to commemorate the only time NATO has invoked its common defense clause; and two chunks of the Berlin Wall to recognize the West’s triumph over communism.

Shooting from the hip

More substantively, Stoltenberg has built consensus among allies to answer Trump’s request, by having each country that has not yet reached the 2 percent target to develop an individual plan by the end of the year showing how the goal will be met by the 2024 deadline agreed on in Wales. If Trump takes that as a win, he will leave Brussels happy. If not, no one quite knows what comes next.

Any calling out of Germany by Trump would not only risk offending Merkel, who is widely regarded as Europe’s preeminent leader; it would also fail to grasp potential misgivings in other European capitals over a heavily militarized Germany.

“Any quick major muscle movement by Germany has repercussions across the Continent and awakens old ghosts,” a senior NATO official said. “And the Germans are very conscious of it. They know the effects.”

The shared costs of maintaining the NATO alliance are relatively small; the lion’s share of spending by allies goes on their own forces, weapons and equipment. And because of Germany’s substantial wealth and its relatively low level of military spending, officials in Berlin say vast sums would be wasted if Berlin rushed to meet the spending target.

In a nod to the politically-charged nature of discussions, Stoltenberg is calling for the individual country plans to be completed by the end of this year, taking the issue off the table in Germany’s upcoming federal elections.

Unlike most of the European leaders dining with him on Thursday, who have spent many years in public service and seek to govern with a measured hand, Trump has no problem shooting from the hip.

Indeed, in a revealing interview with the Associated Press, days after his April 12 meeting with Stoltenberg, Trump conceded he knew little about NATO when he first declared it obsolete.

“I wasn’t in government,” Trump said. “People don’t go around asking about NATO if I’m building a building in Manhattan, right? So they ... asked me about NATO, and I said two things. NATO’s obsolete — not knowing much about NATO, now I know a lot about NATO — NATO is obsolete, and I said, ‘And the reason it’s obsolete is because of the fact they don’t focus on terrorism.’”

The conversation at NATO HQ about terrorism is certain to be colored by Tuesday’s bombing in Manchester, as well as recent terror strikes in Berlin, Stockholm, London, Nice, Brussels and Paris. But while those attacks spotlight the political imperative to fight terror, they also show the potential limits of a multi-national military alliance in addressing local threats.

"He has never dealt with these things. He is coming around to more traditional American positions on these issues" — A senior NATO official

In the AP interview and other public statements, Trump has insisted he is right to press NATO on spending and counterterrorism. And it is this ability of the president to reverse course after reversing course, or to never quite move on — as when he continued to defend Flynn after firing him — that has left NATO officials on edge about how the summit will turn out.

One senior NATO official said Trump had reason to stick to his guns, but expressed hope he would nonetheless side with NATO on the merits.

“I have never heard a U.S. president not talk about burden-sharing or a U.S. defense secretary not talk about burden-sharing and not express frustration,” the official said. “The topic is not revolutionary, the question is just tone.”

“People are explaining these things to him,” the official said. “He has never dealt with these things. He is coming around to more traditional American positions on these issues. They are traditional American positions because they make sense.”