There are some general themes in foreign policy that can be identified. Multilateral engagement is clearly in. Encouraging capable allies to take greater responsibility for regional security issues is in as well. Limited scale is in, open ended commitments and grandiose transformations are out. Aspirational goals are out. Trying to dictate outcomes or the internal policies of foreign nations is out.

I don't know that any of this constitutes a "doctrine" per se; to a large extent it's just an acknowledgment of reality. Given the economic crisis and unproductive legacy wars, the options were fairly limited, and a period of retrenchment and recovery was arguably inevitable. Whether that's simply a period of cyclic reticence in the post-Vietnam mold or the start of a long term decline remains to be seen. That question will ultimately be decided not by US foreign policy decisions, but by America's ability or inability to re-energize its economy. There is likely more hope there than some see: the US has had deep problems before, and has demonstrated the ability to adapt. Adaptation has sometimes been slow and clumsy, with missteps along the way, but that's the nature of adaptation. There are, as always, myriad voices shrieking "doom is nigh and my way is the only way to salvation", but all of them are wrong. Effective adaptation requires a synthesis of multiple competing views, and that sorts out over time.

I do think that this administration's priority on multilateralism is a step in a necessary direction. Like it or not, the world is a multipolar place today, and no nation can aspire to keep peace for all or to play global policeman: the cost is simply too great for any nation to bear alone. There will be no more "Pax Americana"; those days are gone. There could conceivably be a "Pax Democratica", in which the democratic nations of the world cooperate and contribute in ways proportional to their capacity. That's a long way off and it will be a struggle to get there, but at least it's a struggle with a potential future, which a struggle to reverse time and go back to American unipolar primacy would not be. If we can get a few steps down that road, that's something.