Daniel W. Drezner is a professor of international politics at the Fletcher School of Law and Diplomacy at Tufts University and a regular contributor to PostEverything.
Here are President Trump's full remarks from May 25 in Brussels. (The Washington Post)

One of the odder aspects of that very bad, no good, horrible H.R. McMaster and Gary Cohn op-ed of last week was their claim that President Trump had affirmed Article 5 of NATO — “an attack against one ally is considered as an attack against all allies” — when he very clearly had not.

Yesterday, Politico’s Susan Glasser dropped a bombshell of a story that explains why the Trump team’s messaging on this seemed so strange:

The president also disappointed — and surprised — his own top national security officials by failing to include the language reaffirming the so-called Article 5 provision in his speech. National security adviser H.R. McMaster, Defense Secretary James Mattis and Secretary of State Rex Tillerson all supported Trump doing so and had worked in the weeks leading up to the trip to make sure it was included in the speech, according to five sources familiar with the episode. They thought it was, and a White House aide even told The New York Times the day before the line was definitely included.

It was not until the next day, Thursday, May 25, when Trump started talking at an opening ceremony for NATO’s new Brussels headquarters, that the president’s national security team realized their boss had made a decision with major consequences — without consulting or even informing them in advance of the change …

The president appears to have deleted it himself, according to one version making the rounds inside the government, reflecting his personal skepticism about NATO and insistence on lecturing NATO allies about spending more on defense rather than offering reassurances of any sort; another version relayed to others by several White House aides is that Trump’s nationalist chief strategist Steve Bannon and policy aide Stephen Miller played a role in the deletion. (According to NSC spokesman Michael Anton, who did not dispute this account, “The president attended the summit to show his support for the NATO alliance, including Article 5. His continued effort to secure greater defense commitments from other nations is making our alliance stronger.”)

Do read the whole thing.

So why is this such a big deal of a story? The United States is a member of NATO, which means that Article 5 is legally binding whether Trump says so out loud or not. Unlike NAFTA or the Paris climate treaty, I’ve been assured by smart lawyer types that Trump cannot unilaterally withdraw.

So why does this story matter? First, it puts the lie to the notion that Trump can be constrained by the adults in the room. I was dubious of the “Axis of Adults” language when it was first proffered — by last week I was laughing at the lot of them. Still, reasonable people could disagree over whether the mainstream foreign policy folks like Mattis or McMaster could sway Trump when it was important. Given that European allies were clearly fidgety about Trump’s commitment to the alliance, that speech was important.

Second, it makes it clear that Trump possesses core policy beliefs and will stick to them even if given contrary advice by policymakers. On the Paris treaty, this is a guy who “started with a conclusion, and the evidence brought him to the same conclusion,” in the words of Kellyanne Conway. On the Muslim travel ban, this is a guy who tweeted the following last night despite loud warnings from Justice Department lawyers:

As Maggie Haberman tweeted out yesterday morning, “The idea that anyone can stop Trump from doing something once his mind is made up is off.”

Given that Trump’s core foreign policy beliefs are antithetical to the liberal international order, this is going to be a bumpy foreign policy ride.

The real reason Glasser’s story is so devastating, however, is that it undercuts the influence of Mattis, Tillerson and McMaster going forward. In the wake of Trump’s first overseas trip, Mattis tried to do cleanup in Asia, and then Tillerson and Mattis both tried in Australia. To their credit, they said all the right words. Except that those words don’t mean much, since Trump is not listening. They now all sound like Nikki Haley, who is going around sounding thoroughly mainstream but also not necessarily having any influence over foreign policy.

This story is particularly devastating for Tillerson. As Politico’s Eliana Johnson and Michael Crowley reported Sunday, Tillerson has focused all his energies on earning Trump’s trust at the expense of communicating with anyone within his own State Department. He has essentially relied on just two or three key staffers, such as director of policy planning Brian Hook.

That’s a defensible move, if it works. But as Johnson and Crowley noted:

The lack of Trump appointees at the State Department’s regional desks and embassies, and the sidelining of many career diplomats, has added pressure on Hook’s office to develop policy for Tillerson.

It’s also led foreign governments to seek out other avenues of communication. Trump has nominated only a handful of U.S. ambassadors, and some countries have responded simply by reaching out directly to Hook or to other White House officials, including Trump’s son-in-law, Jared Kushner.

If foreign officials were trying to reach Kushner before this story, they are likely redoubling their efforts now. Unless and until Tillerson can demonstrate his ability to shape Trump’s actions, there is not much incentive in talking to him.

There is a vicious feedback loop at work here. Mattis, McMaster and Tillerson lose influence over Trump. This encourages foreign officials to look for their own back channels. This undercuts their influence even more.

Nothing fundamentally changed with this story. And yet, in its own way, it’s a devastating indictment of the influence of Trump’s mainstream policy advisers.