BERLIN (AP) — The steady drum of anti-German rhetoric from the United States, one of the country's traditionally closest friends, has people wondering whether to get ready for a messy breakup.

First, it was then-candidate Donald Trump's campaign trail contention that Chancellor Angela Merkel was "ruining Germany" with her decision to allow in more than 1 million asylum-seekers in 2015 and 2016. Then, as president, came his repeated criticism of the German export surplus with a focus on its popular car brands like Mercedes, BMW and Volkswagen, and the accusation Berlin is shirking its NATO obligations by spending too little on defense.

So everyone thought they were prepared for Trump's arrival at the NATO summit, but were still taken aback by his attack on Germany's energy policy and joint gas pipeline venture with Moscow, which he said it leaves Berlin "totally controlled" and "captive to Russia."

"Trump at NATO Summit: It's not just bad, it's a catastrophe," the influential Sueddeutsche Zeitung headlined its story online.

On the streets of Berlin, people were just shaking their heads.

"A lot of porcelain's being broken at the moment and I think, unfortunately, it will take a while until things that have been broken are fixed again," said Sven Halldorn, 52.

"He should concentrate on his own country before he judges others," added Nicole Urban, 26, echoing a widespread sentiment among Germans.

Many of the issues are not new; former President Barack Obama, who enjoyed a close relationship with Merkel, was critical of the German export surplus, its defense spending and the Nord Stream 2 pipeline project with Russia.

But Trump's increasingly vitriolic tone on those issues, plus his criticism of Merkel's migration policies and his decisions to pull out of agreements dear to Germany like the deal meant to prevent Iran from getting a nuclear weapon and the Paris climate accord, have many questioning what comes next.

"It's an attitude that long term for the German-American relationship is anything but helpful," lawmaker Rolf Muetzenich, a foreign affairs expert with Chancellor Angela Merkel's junior coalition Social Democrats, told the Berliner Zeitung newspaper.

Backing up a step, however, it may be premature to write off the German-American or NATO alliance as some pundits have already been speculating about, said Jessica Gienow-Hecht, a historian of international relations at Berlin's Free University.

"How can you make that point with the little evidence that you have and the fact that there is no alternative planning on the table?" she said. "To me, this is almost like propaganda, it really tells you how far out we're getting here and what sort of an influence that Trump is able to exert."

The development of today's German democracy is in no small way shaped on its relationship with the United States, which helped rebuild the country with the Marshall Plan after the Nazi defeat in World War II, and remained a stalwart friend at the side of West Germany when facing down Soviet aggression during the Cold War.

That doesn't mean there haven't been ups and downs over the decades — seen dramatically after the Sept. 11, 2001 attacks on the U.S. when more than 200,000 Germans took to the streets of Berlin to show their solidarity with the U.S., only to give way a year later to massive demonstrations against the American march toward the invasion of Iraq.

"What we have here is an alliance of necessity, not necessarily a love relationship," said Gienow-Hecht, whose university was established with American support in West Berlin during the Cold War.

She added that the NATO alliance was one built "not because we like each other very much but because we have decided we have similar core values," even if administrations and governments differ from time to time.

Trumps latest comments came as NATO leaders were gathering to meet in Brussels as he met with the alliance's Secretary General Jens Stoltenberg over breakfast. He slammed Germany and Russia's ongoing construction of the Nord Stream 2 pipeline, which will double the amount of natural gas Russia can funnel directly to the heart of Europe when it goes online at the end of next year.

"Germany, as far as I'm concerned, is captive to Russia because it's getting so much of its energy from Russia," he told a stony-faced Stoltenberg, cutting off the NATO chief as he tried to explain allies even traded with Russia at the height of the Cold War. "So we're supposed to protect Germany, but they're getting their energy from Russia. Explain that. And it can't be explained, you know that."

True to form, Merkel, who became chancellor nearly 13 years ago when George W. Bush was president, reacted stoically to the accusation as she arrived at the summit.

Without mentioning Trump or his comments specifically, she noted that she had grown up in communist East Germany behind the Iron Curtain.

"I've experienced myself a part of Germany controlled by the Soviet Union and I'm very happy today that we are united in freedom as the Federal Republic of Germany and can thus say that we can determine our own policies and make our own decisions and that's very good," she said.

The Nord Stream 2 pipeline project, which intentionally skirts Eastern European nations like Poland and Ukraine, has caused many of Germany's allies to bristle, though Berlin has defended it by saying it would be merely one of many sources of natural gas.

Even as Merkel has taken a hard line on Russia in imposing sanctions for its actions in Ukraine, she has kept the $11 billion pipeline off the table.

At the same time, despite his criticism of the pipeline and its links to Russia, Trump has been noncommittal in recent comments about whether he might lift U.S. sanctions on Russia, and told reporters he'd "have to see" whether the U.S. might recognize Crimea to be part of Russia.

By the end of the day in Brussels when Merkel and Trump sat down together, neither seemed interested in continuing the spat — at least not in their public statements in front of the cameras.

Trump said they had a "great meeting" and praised a "very, very good relationship with the chancellor" as well as a "tremendous relationship with Germany," while Merkel said she was happy for the opportunity to talk one-on-one with the president and was "very much looking forward to further" exchanges.

"We are partners, we are good partners, and we will continue to cooperate in the future," she said.