A former commander of NATO said allies of the U.S. are asking whether President Trump was blackmailed by Turkey to pull U.S. military forces out of Syria.

In a CNN segment Monday, Wesley Clark, a retired Army general and former Democratic presidential candidate, said there was no apparent strategic logic for the move that critics view as an abdication to Turkish President Recep Tayyip Erdogan.

"You have to ask why was the decision made?" Clarke said on Christmas Eve. "People around the world are asking this and some of our friends and allies in the Middle East are asking, did Erdogan blackmail the president? Was there a payoff or something? Why would a guy make a decision like this? Because all the recommendations were against it. And it looked like all the facts were against it, too."

"We're not quite finished with we're not taking a lot of casualties over there," he added. "The Kurds have been reliable allies. Why do this right now?"

Trump declared last week the U.S. had defeated the Islamic State and announced the rapid withdrawal of all U.S. ground troops from Syria, where they have been assisting local Kurdish and Arab forces to fight the terror group.

With American forces departing, the U.S. will leave 10,000 Kurdish troops open to attack by Turkey. A senior U.S. official told Jennifer Griffin of Fox News that Trump's announcement Wednesday came after Erdogan told him in a phone call to pull out of Syria because Turkish forces were preparing to assault people tied to the Kurdistan Workers Party, a separatist group the U.S. calls a terrorist organization.

Trump, who made it a campaign promise to wrap up the fight against the Islamic State and bring U.S. troops home said Erdogan assured him Turkey would clean up what was left of the terrorist group.

"President @RT_Erdogan of Turkey has very strongly informed me that he will eradicate whatever is left of ISIS in Syria....and he is a man who can do it plus, Turkey is right 'next door.' Our troops are coming home!" Trump tweeted Sunday after another phone call with Erdogan.

Trump's decision has prompted high-profile exits from top officials in his administration, including Defense Secretary Jim Mattis and Brett McGurk, the special envoy to the counter-ISIS coalition.