You already have a lot of responses, but so far none have included: Trump and some of his top staff are just not that smart. He destroys soft power projection not because he has some thought-out theory about its value, but because he can’t follow the effect chain through far enough to understand the benefits. He really believed Ukraine and Russia were continuing to fight because they hadn’t talked to a skilled negotiator like him: the underlying geopolitics is completely beyond his grasp. He seems to genuinely believe that the spending cuts to Medicaid in his Big Bill will not make millions lose their health insurance.

There are grifters all through the administration and its outside support with the corrupt motives described by other commenters, and Trump himself is greedy and selfish, but I believe he genuinely lacks the intelligence to understand what he is destroying along the way.