If they don't pony up he will gladly begin American withdrawal from Europe

And that will be how he begins to back away from NATO, to back away from globalism.

Trump demands NATO spend more or face shifts in US military

President Donald Trump is demanding that Norway ramp up its defense spending as a NATO partner, according to a letter he wrote to Prime Minister Erna Solberg that was obtained by CNN.

The letter was one of a series that Trump sent to NATO allies, including Germany, Belgium, Canada and others, demanding they boost spending and threatening to shift the US military presence in Europe if they do not. 

The letters were first reported in The New York Times on Monday.

. . . .

In advocating for increased defense spending, Trump joins his predecessors Barack Obama and George W. Bush, both of whom also lobbied NATO allies to spend more on defense. 

Robert Gates, who served as defense Secretary under both Obama and Bush, warned in 2011 that the US could lose interest in NATO if allies did not increase investment in their militaries.