May 11, 2018 The New York Times
President Trump sent two private letters to Middle East allies in recent weeks complaining that the U.S. has spent too much money in the region and urging them to pick up more of the burden as part of a coalition to counter Iran's influence. He has repeatedly said that the U.S. spent $7 trillion in the Middle East since 9/11, referencing a number from the Costs of War Project, which estimates the U.S. will have spent $7 trillion on wars by 2053. According to the institute, current war spending since 9/11 stands at $1.88 trillion.
Trump presses Arab allies to do more to counter Iran (research by Costs of War cited) – The New York Times