European Council President Donald Tusk took US President Donald J. Trump to task on the eve of a key two-day NATO summit that will be held in the European Union’s de facto capital of Brussels from July 11-12, saying the mercurial, isolationist American president to “Appreciate your allies, after all, you don’t have that many”.

In a tone and directness that was decidedly out of character for the notoriously confrontation-averse European Union political establishment, Tusk excoriated Trump for his overtly divisive and belligerent attitude towards the US’ traditional allies and his repeated praise for some of the world’s worst autocrats, including Russian President Vladimir Putin and North Korea’s Kim Jong-un.

“I would like to address President Trump directly, who for a long time now has been criticising Europe almost daily for, in his view, insufficient contributions to the common defence capabilities, and for living off the US,” said a stern Tusk in a strongly worded address. “Dear President Trump: America does not have, and will not have a better ally than Europe,” Tusk added. “Money is important, but genuine solidarity is even more important.”

Tusk particularly addressed Trump’s constant criticisms of the NATO military alliance, which the former has often referred to as “obsolete”.

In his address, Tusk outlined the ways in which the European Union has stood by the US closest ally, including after the 9/11 terror attacks and noted that Europeans spend as much on defence as China, which can field the third-largest military in the world,  and nearly three times as much as Russia, the world’s second-largest military in terms of personnel and the largest nuclear-armed country on Earth.

“Europe was first to respond on a large scale when the US was attacked and called for solidarity after 9/11. European soldiers have been fighting shoulder-to-shoulder with American soldiers in Afghanistan, as 870 Europeans have lost their lives,” before adding, “Dear Mr President, please remember about this tomorrow, when we meet at the NATO summit, but above all when you meet president Putin in Helsinki. It is always worth knowing: who is your strategic friend? And who is your strategic problem?”

The European Union’s overall defence expenditures, which includes five of the 15 largest military forces in the world – France, Italy, the UK, Germany, and Poland. The EU’s collective military budget for 2016 stood at €185 billion, which equalled China’s over the same period and dwarfed Russia’s defence spending of €72 billion at a time when Moscow is actively flexing its military muscles in Ukraine and Syria.

As for the EU-NATO declaration, Tusk said that this move brings the cooperation between the European Union and NATO to the next level in crucially important areas. The agreement includes improving the military mobility of troops and equipment, common preparedness for cyber and hybrid attacks, fighting terrorism and stopping migrant smugglers in the Mediterranean. “The fullest possible involvement in our activities of EU member states that are not NATO members will be encouraged and facilitated in an all-inclusive, non-discriminatory manner, without any artificial obstacles,‘ said Tusk.

Prior to leaving for the summit, Trump took to his preferred medium of communicating his personal opinion on issues that are vital to foreign and domestic policy, saying in a Tweet: “Getting ready to leave for Europe. First meeting – NATO. The U.S. is spending many times more than any other country in order to protect them. Not fair to the U.S. taxpayer. On top of that, we lose $151 Billion on Trade (sic) with the European Union. Charge us big Tariffs (& Barriers)!”

His references to trade and the US’ contribution to NATO have drawn heavy criticism for Trump’s attempt to tie the collective role of NATO – which served as the security framework against a potential threat from the Soviet Union towards the West during the Cold War – with bi- or multilateral trade agreements.

Since becoming president nearly 18 months ago, Trump had shown a woeful lack of understanding about how the NATO alliance works. He has regularly suggested that the US “provides protection” for the other NATO Member States and is regularly “ripped off” by the alliance. A year and a half into his presidency and Trump has not made a single reference to and has shown no knowledge of the founding premise of the alliance, which is collective defence.

Under the NATO charter, all of the 29 members provide mutual protection for one another and all member states contribute to NATO’s overall budget based on their national income, meaning the US’ contribution to NATO is proportional at just over 22% of the overall alliance budget.

Europe plays host to several key NATO air, land and sea bases as well as hosts the alliance’s missile defence shield, and is home to NATO’s headquarters in Brussels. The alliance’s combined military spending accounts for 70% of the global total.

Before departing for Brussels, Trump told reporters that his meeting with Putin, a man who has openly called for the destruction of NATO and who has violated international law by invading and illegally annexing a part of neighbouring Ukraine, the first such act on the European continent since the early years of World War II, “could be the easiest” meeting of his upcoming trip.

“So I have NATO, I have the UK which is in somewhat turmoil, and I have Putin. Frankly, Putin may be the easiest of them all. Who would think! (sic) Who would think. (sic) But the UK certainly has a lot of things going on.”

Many European leaders are deeply concerned that Putin, a skilled geo-political operator, will take advantage of Trump’s personal disdain and lack of knowledge about international affairs and cater to his go-it-alone isolationism by encouraging him to not stand by the US’ key EU allies.