Since Mr. Self asked about Harding, here are some snippets from Harding's Inaugural address.
... The recorded progress of our Republic, materially and spiritually, in itself proves the wisdom of the inherited policy of noninvolvement in Old World affairs. Confident of our ability to work out our own destiny, and jealously guarding our right to do so, we seek no part in directing the destinies of the Old World. We do not mean to be entangled. We will accept no responsibility except as our own conscience and judgment, in each instance, may determine. …
Our eyes never will be blind to a developing menace, our ears never deaf to the call of civilization. We recognize the new order in the world, with the closer contacts which progress has wrought. We sense the call of the human heart for fellowship, fraternity, and cooperation. We crave friendship and harbor no hate. But America, our America, the America builded on the foundation laid by the inspired fathers, can be a party to no permanent military alliance. It can enter into no political commitments, nor assume any economic obligations which will subject our decisions to any other than our own authority. …
We are ready to associate ourselves with the nations of the world, great and small, for conference, for counsel; to seek the expressed views of world opinion; to recommend a way to approximate disarmament and relieve the crushing burdens of military and naval establishments. We elect to participate in suggesting plans for mediation, conciliation, and arbitration, and would gladly join in that expressed conscience of progress, which seeks to clarify and write the laws of international relationship, and establish a world court for the disposition of such justiciable questions as nations are agreed to submit thereto. In expressing aspirations, in seeking practical plans, in translating humanity's new concept of righteousness and justice and its hatred of war into recommended action we are ready most heartily to unite, but every commitment must be made in the exercise of our national sovereignty. Since freedom impelled, and independence inspired, and nationality exalted, a world supergovernment is contrary to everything we cherish and can have no sanction by our Republic. This is not selfishness, it is sanctity. It is not aloofness, it is security. It is not suspicion of others, it is patriotic adherence to the things which made us what we are. …
We must understand that ties of trade bind nations in closest intimacy, and none may receive except as he gives. We have not strengthened ours in accordance with our resources or our genius, notably on our own continent, where a galaxy of Republics reflects the glory of new-world democracy, but in the new order of finance and trade we mean to promote enlarged activities and seek expanded confidence. …
We can reduce the abnormal expenditures, and we will. We can strike at war taxation, and we must. We must face the grim necessity, with full knowledge that the task is to be solved, and we must proceed with a full realization that no statute enacted by man can repeal the inexorable laws of nature.
Our most dangerous tendency is to expect too much of government, and at the same time do for it too little. We contemplate the immediate task of putting our public household in order. We need a rigid and yet sane economy, combined with fiscal justice, and it must be attended by individual prudence and thrift, which are so essential to this trying hour and reassuring for the future. ..."
That strikes me as skeptical of foreign entanglements, but not isolationist. The US started the process of the Washington Naval Arms Limitation Treaty under Harding's Administration and shortly after Harding's death, the US negotiated the Dawes Plan to refinance Weimer germany's debt, so the US was not isolationist.