Trump sends letters to NATO allies demanding more defense spending

"As we discussed during your visit in April, there is growing frustration in the United States that some allies have not stepped up as promised. Continued German underspending on defense undermines the security of the alliance and provides validation for other allies that also do not plan to meet their military spending commitments, because others see you as a role model ... It will, however, become increasingly difficult to justify to American citizens why some countries do not share NATO’s collective security burden while American soldiers continue to sacrifice their lives overseas or come home gravely wounded."

Davis writes that Trump, who used similar language in letters to other leaders, also suggested that the U.S. "might adjust its military presence around the world if its allies do not step and spend more for their own security."

Go deeper: Trump’s letter to Canadian Prime Minister Trudeau, (iPolitics), details of other letters (Foreign Policy.)