It's easy to overemphasize the isolationism of the US in the interwar period. Isolationist is essentially a pejorative term developed to make the views of non-intervention seem more radical than they were. The US remained quite active in international diplomacy during this "isolationist" time. The Washington Naval Treaty, the Kellogg-Briand Pact, the Stimson Doctrine, the Dawes and Young Plans, and many other treaties and policies all show that the US was very involved.
What was not strong was any desire to intervene militarily or be bound by international alliances, which is not just a legacy of WWI and the failure to enter the League of Nations, but part of American culture since the Washington Farewell Address and a feeling of security due to being bordered by two vast oceans. The Great Depression also had a great deal to do with American reluctance to get involved in the problems elsewhere in the world.
It's hard to see how any change about Harding would have changed any of that. Harding was not President when the US declined to do anything with the great crises of the 1930s. And the isolationists leading the America First Committee did not quote Harding, but looked to George Washington's warning about entangling alliances and a general desire to not see the US bombed like how China or Britain were being bombed.
The idea that the US not intervening in WWI means they would be more likely to intervene later is just weird. I think it would just have the opposite effect. "Look, we didn't get involved in WWI, and things turned out just fine. So why do so now?"
The end of traditional American security/alliance policy was the realization that 1) new technologies had made the US less secure behind its oceanic curtain, 2) the threats of the 20th Century (Nazism and Communism) were greater in scope than previous threats, and 3) the US was the only candidate for world leadership after WWII (as neither Britain nor France, the previous leaders were in any shape to do so). The failure of appeasement indicated that the democracies of the world couldn't allow themselves to be picked off one by one, as war would only be delayed and not prevented by such measures.
I would also point out that there were strong anti-interventionist measures in other countries as well during that time including the UK and France. They could have intervened without the US, but did not because of the consequences of what they lost in WWI. Their actions were much more guided by WWI than the US which had longstanding origins.