Trump has long criticized European NATO countries for not spending enough on their own defense, an issue that was largely resolved at last year's summit in the Netherlands, when members agreed to increase their defense budgets.
Now, however, the major challenge remains putting the money into practice. The goal is to quickly strengthen the alliance's military capabilities to meet the growing threat from Russia. But for Trump, money is no longer the main issue.
Iran war
Keeping the US in NATO has been a difficult task for both Mark Rutte and his predecessor Jens Stoltenberg. Already during Trump's first term, he threatened to leave the alliance. During the current term, the challenges have deepened. Last winter, NATO countries were shaken when Trump threatened to take over Greenland from Denmark.
The latest and biggest rift concerns the war against Iran that the US and Israel launched in February of this year.
Trump is deeply dissatisfied that several European NATO countries - including Spain, Germany, Great Britain and France - have refused to provide the United States with sufficient military support, according to his interpretation.
"We don't need their money - we don't need anything. I just want loyalty," Trump said during a meeting with Rutte at the White House in late June.
Praised Erdogan
Trump's frustration has gone so far that he has considered not attending the summit in Ankara on Tuesday and Wednesday.
According to the AP news agency, the American president's respect for Turkish President Recep Tayyip Erdogan is the only reason he chooses to attend at all. During the meeting with Rutte, Trump harshly criticized most European countries, but at the same time praised Erdogan as an "outstanding leader and a good friend."
Trump claimed, among other things, that Turkey could have entered the war on Iran's side because of the country's chilly relationship with Israel, but that Erdogan respected the US's refusal to do so.
For Mark Rutte, Turkey has become a bargaining chip to keep Donald Trump at the negotiating table.
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