February 15, 2016 The Washington Post
Watson's Costs of War project cited in the Washington Post, "As usual, the source of Trump’s claims are unclear. But depending on how you crunch the numbers, his $2 trillion figure for Iraq might be in the ballpark. A 2014 study released by the Watson Institute at Brown University said the amount spent on the wars in Afghanistan and Iraq through fiscal year 2014 was nearly $1.6 trillion."
Fact checking the ninth GOP debate (Costs of War study cited) – The Washington Post