Even before the 2016 elections, many of us were predicting that the U.S. would go through a period of retrenchment in terms of its global engagement--that a combination of rising costs and the emergence of alternative power centers in the international system would impose limits on America's freedom of action to set the global agenda--but that the United States would not undertake a complete withdrawal. The election of Donald Trump introduced the "America First" element--the notion that U.S. engagement would be judged on more transactional criteria in terms of short-term, immediate benefits to the United States, rather than on whether it supported the emergence of enduring architecture that would advance longer-term values.
Now, there is a concern that the United States is indeed embarked on a policy of disengagement, disconnecting itself from multilateral institutions and procedures that, in some cases, it had taken the lead role in creating. Richard Haass, of the Council on Foreign Relations, has termed this tendency of the new administration as "the withdrawal doctrine." Some of the withdrawals are to be expected, as they were commitments made by previous administrations on the basis of Presidential executive authority, in part because passage through the traditional Congressional ratification process would not have been forthcoming. Indeed, the massive expansion of executive authority in the last several Presidential administrations (in terms of binding agreements and even the war power) has created precedents that other presidents can utilize to move American policy in different directions. But the Trump administration is also questioning the strategic and even philosophical basis of the doctrine of "democratic enlargement" which has been the primary post-cold war guide to U.S. strategy.
But it is not clear at all that the Trump administration is isolationist in its approach. The withdrawal strategy seems to be a prelude to renegotiating the terms of American engagement in the world--but with a new emphasis on the mercenary aspects--that is, that the Trump administration expects other states to compensate the U.S. for the tasks it takes in order to sustain and support the current global order--and that, in the event of nonpayment, the U.S. would be prepared to withdraw.
In the past, the U.S. never engaged in open transactionalism in its foreign policy because U.S. engagement--military alliances and free trade arrangements with other states--generated concrete benefits for the average American to sustain public support for U.S. leadership. It is because, in recent years, that perception has changed that the transactionalist ethos has gained strength--and the first fruits of its approach are now being realized.