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U.S. Ambassador Bill Roebuck, the special envoy for the anti-ISIS campaign in Syria, sent a scathing memo to the Trump administration, criticizing it for not doing enough stop the Turkish-backed military assault into the Syrian border.

The 3,200 word memo, which was obtained by The New York Times, was dated October 31 and delivered to representatives in the State Department, the White House, and Defense Department. Titled “Standing By as Turks Cleanse Kurds in Northern Syria and De-Stabilize our [Defeat ISIS] Platform in the Northeast,” Roebuck questioned the U.S/'s efforts to dissuade Turkey from sending militants to the border and said it was a “tough call” in determining whether it would have prevented Turkey's offensive earlier in October.

“But we won't know because we didn't try,” Roebuck reportedly said in the memo.

President Donald Trump's decision to withdraw U.S. troops from key positions in the Turkey-Syria border effectively green lit Turkish President Recep Tayyip Erdogan's longtime plan to attack Kurdish positions near the border.

Turkey has long viewed members of the Kurdistan Workers' Party (PKK) as a terrorist threat and has hunted them in other countries, including Iraq. After thousands of people were killed in the decades-long conflict between Turkey and the PKK, Erdogan vowed to stem the Kurdish influence near his border. Turkey claims the Kurdish People's Protection Units, or YPG, and the Kurdish-majority Syrian Democratic Forces are a threat with links to the PKK.

“I do not say there were easy choices here in Syria and that we failed to make them because of ignorance or bad intentions or lack of resolve,” Roebuck wrote. “U.S. policy makers, coalition diplomats and their leaders, have done their best to contain the maelstrom that Syria has become.”

“This situation on the northern border is in some ways a sideshow of that larger catastrophe,” Roebuck added. “But it is a catastrophic sideshow and it is to a significant degree of our making.”

Following a phone call with Trump, President Erdogan directed Turkish-backed militants towards the border, where human rights violations against the Kurds have reportedly taken place, including extrajudicial killings of civilians. The U.S. and Turkey have since signed an agreement to a ceasefire in the region, which some Republicans have likened to a “surrender” due to the eviction of Kurdish groups.

Kurdish militants have been backed by the U.S. and have spearheaded the fight against ISIS in Syria. The U.S. relied on roughly 60,000 Kurdish troops to reclaim territories once held by the terrorist group. Around 11,000 Kurds have died in the conflict.

“One day when the diplomatic history is written, people will wonder what happened here and why officials didn't do more to stop it or at least speak out more forcefully to blame Turkey for its behavior: an unprovoked military operation that has killed some 200 civilians, left well over 100,000 people (and counting) newly displaced and homeless because of its military operation,” Roebuck wrote.

Roebuck adds that Trump's decision to protect oil fields in northern Syria is “a good one,” but adds it may “play into toxic Middle Eastern conspiracy theories that will need to be lanced with careful, sustained messaging reinforcing the truism that Syria's oil is Syria's and for the benefit of the Syrian people.”

In late October, Trump reversed course and deployed additional troops and armored vehicles to Syria to “keep the oil.”

Pentagon officials on Thursday said that the oil fields, which have been operated by the SDF after being reclaimed from ISIS, would continue to be used by the Kurdish-majority group. Pentagon officials added that the revenue would not go to the U.S., but continue to be streamed to the SDF.

Roebuck's memo echoes the opinion of other lawmakers from both parties, foreign policy experts, and military officials who have been outspoken against the sudden withdrawal of U.S. troops in the region. Trump's staunchest allies have been critical of the withdrawal, citing the potential resurgence of the Islamic State amid the chaos, and the abandonment of the once-U.S.-backed Kurdish allies.

“This impulsive decision by the president has undone all the gains we've made, thrown the region into further chaos, Iran is licking their chops, and if I'm an ISIS fighter, I've got a second lease on life,” Republican Sen. Lindsey Graham of South Carolina said during a Fox News interview on October 7.

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