According to former White House national security adviser John Bolton in his book, The Room where it happened: the White House memoir, Trump wanted to threaten NATO leaders at the 2018 summit with the US leaving the Alliance if they did not pay contributions of 2% of GDP. According to him, after that, he discussed Trump’s threat to withdraw from NATO with Secretary of state Mike Pompeo; they decided to convince him to stay in the Alliance, but perhaps by reducing US contributions. As a result, in his speech, Trump did as Bolton advised him – he declared his support for NATO, but criticized those countries of the Alliance that still have small defense budgets.
In an interview with Thyssen, Trump complained that 2% of GDP is also “too little.”
“There were those who paid almost nothing, and now they are paying. And they asked me an important question: “You would leave if…” and I answered: “Yes, I would leave.” And if you don’t give that answer, they’re not going to pay,” said Trump, whose words are quoted by Thyssen in his article published by the Washington Post.
When asked by a columnist whether Trump wants the US to leave NATO, Trump replied in the negative. “No, I don’t want to leave… But I want them to pay their fair share,” Trump said.