This is too simplified of an answer.

It may be the case that his base is still just following him and supportive of whatever he does.

But the number of people who voted for him vastly exceeds his “base”, and the entire MAGA movement is basically predicated on a form of isolationism, or at least not pro-intervention. Part of the reason it became popular was as a reaction against the wars in Iraq and Afghanistan.

So I don’t think it’s as simple and one dimensional as you paint here. Which is exactly why I think it’s a systemic problem: many people probably voted for him because of the campaign promises of being against foreign wars.