NATO summits are designed to be dull demonstrations of unity and purpose. Mainly thanks to President Trump, not this time.

Before leaders of the alliance’s 29 member states had even filed into the North Atlantic Treaty Organization’s new headquarters, they split over at least three issues: burden sharing, a planned natural gas pipeline between Germany and Russia, and Turkey’s purchase of Russian anti-aircraft missile systems.

In the early hours on Thursday, Trump returned to the attack: “Billions of additional dollars are being spent by NATO countries since my visit last year, at my request, but it isn’t nearly enough,” he tweeted. “U.S. spends too much. Europe’s borders are BAD! Pipeline dollars to Russia are not acceptable!”

Few had expected smooth sailing at the Brussels summit. But the vehemence of Trump’s on-camera breakfast attack on Germany for its backing of a second Nord Stream gas pipeline, and for being “captive” to Russia came as a shock. German Chancellor Angela Merkel on Wednesday gave Trump an uncharacteristically personal response, reminding him that she knew what captive means, having grown up in Soviet-controlled East Germany.

“So we’re supposed to protect you against Russia, and they’re paying billions to Russia,” Trump told NATO Secretary General Jens Stoltenberg at the start of their breakfast meeting. He went on to suggest that it wasn’t only the projected Nord Stream 2 pipeline that he had in his sights, but German purchases of Russian gas as a whole. “Germany is totally controlled by Russia,” he said.

That broadside quickly rifled through the conference, forcing countries to pick sides – even though the Soviet Union supplied western Europe with gas throughout the Cold War without interruption. Asked if he thought Germany was captive to Russia, French President Emmanuel Macron responded with a short “no.”

It also drew a rare partisan rebuke for a U.S. president’s actions while still overseas. In a joint statement, Democratic congressional leaders Nancy Pelosi and Chuck Schumer called Trump’s remarks “another profoundly disturbing signal that the president is more loyal to President Putin than to our NATO allies.”

Trump will meet with Russian President Vladimir Putin in Helsinki on July 16.

Trump continued his criticism of other NATO countries for failing to meet their 2 percent of gross domestic product defense spending targets fast enough, and then on Twitter proposed doubling the target. His assault on Germany over Nord Stream found more backers.

Poland’s Foreign Minister Jacek Czaputowicz sided with Trump, attacking German Defense Minister Ursula von der Leyen for Germany’s support for construction of the first phase of Nord Stream, as well as the planned addition. Speaking at a morning panel session at a side conference organized by the Atlantic Council, a Washington think tank, Czaputowicz alleged that the pipeline’s revenues had funded the modernization of Russia’s military.

On another front, the purchase of NATO incompatible S-400 missile systems from Russia, Turkish Foreign Minister Mevlut Cavusoglu attacked Germany’s defense minister for withdrawing Patriot missile defense systems away from Turkey’s border with Syria, forcing Ankara to look at buying its own. When von der Leyen responded that it was simply a rotation, Cavusoglu replied tartly that Italy had extended its rotations “like a real ally.”

Stoltenberg’s response to Trump on Wednesday morning – that the alliance was one of 29 nations that needed to remain unified to remain strong, despite disagreements – reflected a deeper concern: That Trump’s public sowing of division could damage the projection of unity that is the cornerstone to NATO’s primary task, deterrence.

“Russia is looking for opportunities,” Lithuanian Defense Minister Raimundos Karoblis said during a discussion on defense deterrence at the side conference. “We need to be very careful of that.”

Stoltenberg and others stressed that despite Trump’s tweets and verbal attacks, the leaders would be rolling out important new measures to beef up the defense of NATO’s eastern flank, and that the U.S. itself has spent 40 percent more on Europe’s defenses since Trump came into office.

They also recalled that NATO disputes are hardly new. Danish retired general Knud Bartels recalled bitter divisions over support for the U.S. war in Vietnam in the 1970s, as well as over stationing of Pershing missiles in Germany in the 1980s. And behind closed doors the atmosphere “was more relaxed than what’s been said,” Macron told reporters as he returned to the summit on Thursday.

“We should be careful not to dramatize,” said Bartels, now adjunct professor at the Royal Danish Defense College. “It has never been easy.”

But with the Cold War over and Russia contesting borders in Ukraine and Georgia, the alliance may also be more fragile than it was during previous, arguably more substantive disputes. Whatever Trump’s intent, the public message being sent out – that he considers Germany a competitor rather than an ally, and treats U.S. support for NATO as conditional – will be watched carefully from the Kremlin, said Pavel Felgenhauer, a Moscow-based military analyst with the Jamestown Foundation.

He warned of the potential for further Russian military moves in Ukraine, especially if the U.S. should become more engaged in conflicts in the Middle East where it needs Russia’s cooperation, and Putin calculates he has freedom to act without U.S. retaliation.

“What is really serious is that the credibility of NATO as a deterrent is being weakened,” Felgenhauer said. “That can make the world more unpredictable in a major way.”

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