President Donald Trump on Thursday delivered a speech at NATO headquarters in which he did not explicitly endorse Article 5, which outlines a policy of collective defense among all members of the alliance.

While this might seem like a small oversight to casual observers, Brookings Institute fellow and top foreign policy scholar Tom Wright said Trump’s refusal to endorse Article 5 has rendered his entire foreign policy trip a “failure.”

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“The White House told the NYT yesterday Trump would finally endorse Article 5,” he wrote on Twitter. “The fact that he did not is astonishing and shows that someone in the White House or [Trump] himself took it out. This will come as a huge shock to NATO members.”

Wright went on to say that Trump’s trip can now be considered “close to a disaster” unless he explicitly fixes things by endorsing Article 5 later on Thursday. He also said that Russian President Vladimir Putin “will be thrilled at Trump’s refusal to endorse Article 5,” which he described as “unimaginable under any other president.”

Read the whole tweet storm below.

Trump does not mention Article 5 in his speech. Wow. Vague mention of commitments in passing. Shocking and damaging. — Tom Wright (@thomaswright08) May 25, 2017

The White House told the NYT yesterday Trump would finally endorse Article 5. The fact that he did not is astonishing and shows 1/n — Tom Wright (@thomaswright08) May 25, 2017

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Trump's trip had been a relative success until now. It is now a failure. Close to a disaster unless he fixes it later today 3/3 — Tom Wright (@thomaswright08) May 25, 2017

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Putin will be thrilled at Trump's refusal to endorse Article 5. Unimaginable under any other president. — Tom Wright (@thomaswright08) May 25, 2017