(BRUSSELS) — President Joe Biden on Monday called NATO’s Article 5 — which states an attack on one member nation is an attack on all — “a sacred obligation,” and NATO was poised to update how it will respond jointly to cyberattacks.

“I constantly remind Americans that when America was attacked for the first time on its shores since what happened back at the end of World War II, NATO stepped up,” the president said in a meeting with NATO Secretary General Jens Stoltenberg in Brussels, referencing the 9/11 terror attacks.

“I just want all of Europe to know that the United States is there. The United States is there.”

Biden’s endorsement of NATO stands in stark contrast to his predecessor, former President Donald Trump, who called the alliance “obsolete,” which he later backtracked, and once declined to endorse Article 5, which has been a key tenet of the alliance since it was created in 1949.

On Sunday, White House National Security Adviser Jake Sullivan suggested that the communique released at the end of the NATO summit could include language to update Article 5 to now include the growing global threat of cyberattacks.

“This would be on a case-by-case basis,” he said. “And the notion is that if someone gets hit by a massive cyberattack, and they need technical or intelligence support from another ally to be able to deal with it, they could invoke Article 5 to be able to get that.”

Following his meeting with Stoltenberg, Biden kicked off the first day of the NATO summit by sending a clear message to Russian President Vladimir Putin that he intends to stand up for threatened nations in Russia’s backyard — and met with the leaders of Estonia, Latvia and Lithuania, expressing support for their security.

“It was a constructive, warm, vigorous engagement between him and the three leaders and a real show of solidarity and unity with NATO’s eastern flank,” a senior administration official said.

Biden previewed his upcoming meeting with Putin during his meeting with Baltic leaders, discussing “the threat that Russia poses,” the official said, and also brought up the recent “air piracy” that occurred when a Ryanair flight was forced to divert and land in Belarus — which was originally bound for Lithuania.

“The four leaders committed to further strengthening our political, military, and economic partnerships, including working together through NATO to address challenges posed by Russia and China,” the White House said in a written statement following their meeting.

He also met with the president of Poland and Romania in separate, brief meetings Monday at NATO headquarters.

Biden will be holding a solo news conference following his summit with Putin in Geneva on Wednesday, defending that choice by saying he doesn’t want the attention to be on physical details, but rather the substance of their discussions from their own points of view.

“I don’t want to get into being diverted by, did they shake hands? How far did they — who talked the most and the rest,” Biden said in England on Sunday. “He can say what he said the meeting was about and I will say what I think the meeting was about. That’s how I’m going to handle it.”

Biden is also expected to hold a one-on-one meeting with Turkish President Recep Tayyip Erdogan Monday afternoon, amid strained relations between the two countries.

In April, Biden became the first sitting U.S. president to formally recognize the Ottoman Empire’s killing and deportation of Armenians over a century ago as genocide, breaking from his predecessors and risking inflaming tensions with Turkey, a key NATO ally, who warned against it.

The U.S. also angered Turkey over the decision to cancel its participation in the F-35 fighter jets program last year after they accepted a Russian-made air defense system.

When the two spoke on April 23, Biden expressed his interest in the “effective management of disagreements,” according to a White House readout of their call.

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