In the "never apologize, never explain" genre of bad business school books from the 1970s, Trump absorbed approximately one thing: Every deal must have a winner and a loser. There's no such thing as a mutually beneficial agreement, and if Trump is in an agreement where the other side is deriving some benefit, it must be a bad deal for him to be involved in. So the deal has to be blown up and renegotiated in his favor, and his favor alone.
Relative peace in Europe for the last 70 years is seen as no personal benefit to Trump (yes, there have been battles and wars in Europe since World War II ended, but none of them spread into continent-wide conflagrations as they used to do with depressing regularity). So NATO must be dismantled and recrafted on far more favorable terms. If Europe gets destabilized, so much the better, because Trump thinks it will get them back to the bargaining table that much faster and more eager to deal on his terms. On first meeting Angela Merkel, Trump reportedly told her that Germany owed him $1 trillion. Note that he wasn't talking about the United States, but him personally. But it was just a joke. Of course. From a man who never laughs.
The next time Trump goes off the rails, I'd give a dollar to the person who interrupts him and says, "Clearly you don't know what you're talking about."