That was clear from the very beginning that the costly program to train 'good' rebels to fight 'bad' ones was doomed to failure. The Pentagon planned to spend half a billion dollars on the program. The U.S. has already faced misfortunes like that in its history. As we know, Washington took part in the creation of Al-Qaeda, the largest terrorist organization in the world until now. But as soon as the fighters got stronger they turned their weapons against the Americans.
The same situation is developing around the so called New Syrian Force. Returning to Syria the Pentagon-trained rebels joined the organization they were supposed to struggle.
It is hard to escape a conclusion that the U.S. doesn't learn from its own mistakes. But the situation may be much more complex. Given the Pentagon's great experience in covert operations it may appear that the U.S. special services planned the rebels would turn the side beforehand. To cover this fact the U.S. defense and state departments usually very sophisticated in concealing or justifying their failures were easy to accept their mistake this time.
The Islamic State that was supposedly also created by Washington has been in great need of qualified personnel of late to operate the U.S. weapons and equipment lost or intentionally left by the Iraqi forces retreating from Mosul in June 2014.
Haider al-Abadi, the new Iraqi prime minister, announced in the early June 2015 that terrorists had captured a great number of U.S.-made weaponry including 2,300 Humvee armored vehicles, at least 40 M1A1 main battle tanks, 74,000 machine guns, and as many as 52 M198 howitzer mobile gun systems, plus small arms and ammunition. The U.S. mass media wrote that "the U.S. has armed ISIS".
Several dozen people that joined the ISIS would hardly change the situation in Syria but they evidently were not supposed to. They may become instructors and train Islamic State fighters to use American weapons.
However, the U.S. is playing very dangerous games with terrorists. The Washington's model of controlled chaos in the Middle East may go out of order at any moment and hit the Americans back. In that case thousands of people would pay with their lives for all those covert operations.