Depending on who you read the US Defense Secretary either decided to retire early or was fired. He never seemed to have quite the grip of some of his predecessors, but US strategy has been less clear cut. The aftermath of Iraq and Afghanistan coupled with the total failure of the expected outcome in Libya and the fragmented nature of the western backed opposition to Assad which allowed the rise of ISIS, all roll up into a muddled package of uncertainty and failure. On the positive side, although extended and long winded, the talks with Iran are a major achievement.
The reason that the Pentagon is unhappy is that US public opinion will not back any more wars which involve sacrificing its young men in countries riven by internal quarrels. So whatever the preference for ground forces in the Middle East, it is not going to happen. It will be interesting to see whether the appointment of former Obama challenger and super hawk, the Arizona Senator John McCain, to chair the powerful Senate Armed Services committee will make American public opinion more pro boots or more anti.