Istanbul — There are new tensions between the U.S. and Turkey, a key NATO ally, after national security adviser John Bolton came here to discuss the timing of the U.S. withdrawal from Syria. Bolton was looked for assurance that when the U.S. pulls its roughly 2,000 troops out of neighboring Syria, the Turkish will not attack Syrian allies of the U.S. on the ground.

Instead, an angry Turkish President Recep Tayyip Erdogan accused Bolton of making a "serious mistake" after mixed messages on the U.S. withdrawal plan.

U.S. partners in Syria are fighters from a local militia group still battling ISIS holdouts in the desert. But Turkey views them as a terrorist organization, and says it has drawn up plans to attack them.

Less than a month after President Trump announced that American troops in Syria would be coming home, there's now confusion over exactly when they'll withdraw, leaving U.S. allies unsettled in the Middle East.

Meanwhile, U.S. partners in the fight against ISIS, known as the Syrian Democratic Forces, also feel betrayed. They've called the U.S. withdrawal a "stab in the back" and fear an onslaught from Turkey.

CBS News has witnessed the ragtag army of farmers, students and shopkeepers. In 2017, a U.S. commander explained how crucial their role was.

"Our Syrian partners here are doing the world's bidding, the world's fight. They're doing what no one else is willing [to do] or capable of [doing]," said Gen. Stephen Townsend.