Updated at 5:07 p.m.

BRUSSELS — President Trump did not explicitly endorse the mutual-aid clause of the North Atlantic Treaty at the NATO summit on Thursday despite previous indications that he was planning to do so, keeping in place the cloud of ambiguity hanging over the relationship between the United States and the alliance.

Speaking in front of a 9/11 and Article 5 Memorial at the new NATO headquarters, Trump praised NATO’s response to the 9/11 attacks and spoke of “the commitments that bind us together as one.”

But he did not specifically commit to honor Article 5, which stipulates that other NATO allies must come to the aid of an ally under attack if it is invoked.

The only time in history that Article 5 has been invoked was after the September 11 attacks, a fact that Trump mentioned. The memorial Trump was dedicating is a piece of steel from the North Tower that fell during the attacks.

“We remember and mourn those nearly 3,000 people who were brutally murdered by terrorists on September 11, 2001,” Trump said. “Our NATO allies responded swiftly and decisively, invoking for the first time in its history the Article 5 collective-defense commitment.”

Trump did refer to “commitments,” saying of the memorial, “[t]his twisted mass of metal reminds us not only what we’ve lost, but forever what endures: the courage of our people, the strength of our resolve, and the commitments that bind us together as one. ... We will never forsake the friends who stood by our side. And we will never waver in our determination to defeat terrorism and to achieve lasting prosperity and peace.”

The New York Times reported on Wednesday evening that Trump would use the speech to finally endorse Article 5. Though top members of his administration, including Defense Secretary Jim Mattis and Vice President Mike Pence have done so, Trump’s refusal has shaken NATO allies.

Trump has been a harsh critic of NATO overall, at one point calling it “obsolete.” He has repeatedly criticized other allies for not paying their fair share of the defense burden of the alliance. He has pushed the alliance to do more to combat terrorism. At the NATO leaders summit, counter-terrorism and burden-sharing will dominate the agenda—not Russia.

Trump did mention the Russian threat in his remarks on Thursday. “The NATO of the future must include a great focus on terrorism and immigration, as well as threats from Russia and on NATO’s eastern and southern borders,” he said.

But he spent the bulk of the speech haranguing the other members of the alliance—standing only feet from him—for not meeting their spending obligations.

“Twenty-three of the 28 member nations are still not paying what they should be paying and what they are supposed to be paying for their defense,” Trump said. “We should recognize that with these chronic underpayments and growing threats, even two percent of GDP is insufficient to close the gaps in modernizing, readiness and the size of forces,” he added. “Two percent is the bare minimum for confronting today’s very real and very vicious threats.”

Trump even took a slight dig at the new NATO headquarters, which are being unveiled in time for this leaders’ meeting. “I never asked once what the new NATO headquarters cost,” Trump said. “I refuse to do that. But it is beautiful.”

After the speech, televisions in the press center at NATO showed Trump in discussion with a group of other leaders including NATO Secretary General Jens Stoltenberg and German Chancellor Angela Merkel.

NATO had sought to make Trump’s inaugural visit as smooth as possible. The conference’s two topics of focus—spending and counterterrorism—are the two main thrusts of Trump’s critique of the alliance.

White House press secretary Sean Spicer, speaking to the pool reporters after the speech, said that despite the president’s  omission, “We’re not playing cutesy with this. He’s fully committed.”

“If you are standing at a ceremony talking about the invocation of Article 5 after 9/11 and talking about that, that is a pretty clear indication of the support that exists for it,” Spicer said. “I’ve seen some of the questions I’ve gotten from you guys, but there’s 100 percent commitment to Article 5.”

In a press conference on Wednesday before the summit, Stoltenberg had downplayed Trump’s silence on Article 5. He said that because Trump has expressed support for NATO—which he declared no longer obsolete during Stoltenberg’s visit to Washington last month—he “has also of course expressed strong support of Article 5, because Article 5, collective defense, is NATO’s core task.”

At a press conference after the leaders’ meeting on Thursday, Stoltenberg was asked repeatedly about Trump’s refusal to verbally commit to Article 5. He maintained his position, arguing that Trump has shown sufficient commitment to NATO, and thus to Article 5. “President Donald Trump dedicated a 9/11 and Article 5 memorial,” Stoltenberg said. “And just by doing that he sent a strong signal. … We have had a clear message from the U.S. administration,” he added, citing assurances he received from top administration officials as well as from Trump himself in meetings. “It’s not possible to be committed to NATO without being committed to Article 5.”

Asked if Trump’s demands about burden-sharing had troubled any allies, Stoltenberg said they had already heard Trump being “blunt” on spending before. “We have to invest in defense not just to please the United States but we have to invest in European defense because it is in our own interest to do so,” he said.