Because isolationism worked out so damned well for us 90 years ago?
This isn't new. The FlatulenT Rump administration absolutely gutted the state department their first time in office, leaving posts unfilled, losing institutional memory and connections that I'm certain have damaged our standing in the world ever since.
"I have nukes" is his idea of diplomacy. And while the threat of force/lawsuits works at one level... like a high school bully who painted themselves into a corner without any skills who ends up as a drunk gas station attendant with a miserable fading trophy wife who thought he was going places... he's now parked in a job he clearly doesn't like, knocking down institutions left and right so that he can get money for his self-aggrandizing monuments to meaningless self-given trophies.
Maybe we couldn't keep funding the state department at the level we had been, who knows, but he's not smart enough to know that, or to adequately weigh the cost benefit to the nation without a strong investment in international relations.
But whatever history books are supposedly printed on, will remember his name and face as "The Death of U.S. Supremacy".
Fuck him and his torched and salted legacy.