The top American diplomat stationed in northern Syria slammed the Trump administration for not trying hard enough to deter Turkey’s military offensive last month, according to an internal memo obtained by The New York Times. The memo, penned by diplomat William Roebuck, questioned whether tougher American diplomacy could have deterred Turkey from attacking last month and committing “war crimes and ethnic cleansing.”

“It’s a tough call, and the answer is probably not,” Roebuck wrote in the memo, according to the report. “But we won’t know because we didn’t try.”

Roebuck, however, did note several reasons the Turkish regime may have not been deterred, including the small U.S. military presence and the country’s standing as a NATO ally. The diplomat also said the Trump administration’s actions left Syrian Kurdish allies abandoned, which has essentially opened the door for a possible Islamic State resurgence.