The studies were initiated after Trump’s expressed his interest in pulling out US forces at a meeting earlier this year with White House and military officials, the newspaper said, citing unnamed US officials.
Trump was taken aback by the cost and size of the US presence, which includes 35,000 active-duty troops, the report added.
Meanwhile, Trump has reiterated NATO allies need to increase defense spending, ahead of the alliance’s summit in Brussels next month. "Germany has to spend more money, Spain, France, it's not fair what they've done to the United States," he said Friday.
He claimed the United States was paying "much more disproportionately to anyone else" in the alliance, which sets a spending target of 2 percent of a member state’s gross domestic product.