A  heated verbal exchange broke out between Turkish Foreign Affairs Minister Mevlut Çavuşoğlu and Germany’s Minister of Defence, Ursula von der Leyen over a decision by the Turkish government to purchase Russia’s S-400 anti-aircraft system S-400 kicked off the two-day NATO Summit that in Brussels on July 11, sending a new dangerous signal to the West’s adversaries that all is not well amongst the group of long-time allies.

Following the exchange, Ali Aslan, a German of Turkish origin and a reporter for Germany’s DW news outlet and the moderator of a panel discussion between von der Leyen, Çavuşoğlu and Polish Foreign Minister Jacek Czaputowicz, cut into the heated exchange between von der Leyen and Çavuşoğlu in an attempt to calm the situation. Çavuşoğlu, however, snapped back at Aslan, telling him to keep in mind a case involving Deniz Yücel, another German journalist of Turkish descendant who also worked for DW and spent a year in Istanbul’s notorious Silivri Prison after he was accused, though never charged, by Turkey’s autocratic President Recep Tayyip Erdogan of working for German intelligence and for sympathising with banned Kurdish parties, including the PKK.

“NATO is able to cover only 30% of Turkey’s airspace and who will cover the rest? Who is going to protect my nation, my people, from the missiles coming from Syria or any other countries?” We tried to buy from the UK, France, the US, and even China, but we were rejected. Eventually, we got the best deal from Russia,” Çavuşoğlu said, adding that the purchase was necessary after Germany “withdrew” its Patriot missiles from Turkey’s southern border.

When von der Leyen contradicted Çavuşoğlu’s account, saying that Germany and several other NATO allies, including the United States and the United Kingdom, have regularly patrolled the Turkish-Syrian border for three years from the huge NATO airbase located at Incirlik in southeast Turkey and argued that the withdrawal of Patriot missile batteries as part of a regular rotation of NATO defence systems, Çavuşoğlu fired back that alliance members Spain and Italy “prolonged their planned rotations like real allies.”

 Ankara’s purchase of Russia’s S-400 air defence systems has deeply angered Turkey’s allies in NATO, while the conservative Islamist Erdogan’s close relationship with Russian President Vladimir Putin has raised serious questions about Turkey’s credibility as a reliable ally for the other NATO members.

Erdogan signed a $2.5 billion agreement with Moscow for S-400s in September of last year as part of his government’s plan to boost its defence capabilities outside of the NATO command structure in what Erdogan claimed was an attempt counter threats from Kurdish militias and ISIS.

The deal was resoundingly condemned by other NATO members, who said the purchase was a major security breach and a violation of the alliance’s collective security umbrella. Many key NATO members are deeply concerned by Moscow’s military presence in the conflict in Syria as well as the Kremlin’s build-up of rapid response forces on the European Union’s borders and the deployment of ICBMs in Russia’s Kaliningrad exclave on the Baltic Sea and on the Crimea Peninsula, which Putin invaded and illegally annexed from Ukraine in March 2014., followed by warning about unspecified consequences of purchasing the S-400.

Erdogan has tried to calm his Western partners’ concerns about the acquisition of S-400s, saying Turkey’s ties to NATO remain strong.

Despite the acrimonious tone between the three ministers, each stressed that NATO needed to adapt for the future and to maintain Trans-Atlantic unity to keep the Alliance together. The challenge, as was plainly on display during the panel discussion, will be to get the 29 NATO members to agree on what the main threat to NATO is particularly at a time when the alliance’s largest contributor, the United States, is led by an isolationist president with a vitriolic disdain for international alliances and who has openly questioned whether the US will continue as a member of NATO.

As the panel’s forceful champion of maintaining unity, von der Leyen concluded the discussion by saying, “it is up to our generation now to renew that [unity], because I want my children in fifty years to live under the security umbrella of NATO in a democracy…that is worth fighting for.”

Von der Leyen’s comments came after US President Donald J. Trump launched into an unhinged tirade against Germany — the largest and richest NATO ally after the United States as the world’s fourth-largest economy which can field the eighth largest military — and other NATO allies for what he believes is their attempt to live off the US’ protection, without contributing to their own defence.

“So we’re protecting Germany, we’re protecting France, we’re protecting all of these countries. And then numerous of the countries go out and make a pipeline deal with Russia where they’re paying billions of dollars into the coffers of Russia,” Trump continued. “And I think that’s very inappropriate,” Trump said in reference to the controversial Nord Stream-2 gas pipeline that will send Russian natural gas to the European Union via an underwater pipeline in the Baltic Sea.

The European Union and NATO are worried Nord Stream-2 will give Gazprom a stronger position on the EU’s gas market. But by linking NATO’s founding principle of collective defence to business deals by the individual members, Trump is actively threatening to scuttle the cohesiveness of the alliance due to his inability to understand NATO’s founding principles, which are not linked to business of trade, but that the West can help protect itself through a common security umbrella.

NATO Secretary-General Jens Stoltenberg, who was visibly taken aback by Trump’s diatribe, had hoped to convince the mercurial US president that other key NATO allies are responding to his repeated demands for increased defence spending and have already allocated significant funds to contribute to the alliance.

“You can spend 2% on your national defence budget without doing anything for NATO,” she said, after noting that Germany has contributed the second-highest number of troops to the Alliance and is the second-largest net payer after the United States,” Germany’s von der Leyen said.